Stop releasing Swift extension CocoaPods

[paulb777]

10.18.0 will be the last release of the Swift extension CocoaPods. They can continue to be used as no-ops through the lifetime of 10.x. We plan deprecate those pods after the new year.

#no-changelog (follow up to 10.17.0 consolidation changelogs)

[paulb777]

I'll remove the Swift pods from SpecsStaging after this merges

[ncooke3]

FYI, I did seem remaining references to extension specific logic:

> git grep Swift ReleaseTooling/Sources/
ReleaseTooling/Sources/FirebaseReleaser/InitializeRelease.swift:    updateSwiftPackageVersion(path: gitRoot, version: manifest.version)
ReleaseTooling/Sources/FirebaseReleaser/InitializeRelease.swift:  // This function patches the versions in the Firebase.podspec. It uses Swift instead of sed
ReleaseTooling/Sources/FirebaseReleaser/InitializeRelease.swift:  // TODO: If we keep Swift, consider using Scanner.
ReleaseTooling/Sources/FirebaseReleaser/InitializeRelease.swift:        // TODO: This block is redundant with `updatePodspecs`. Decide to go with Swift or sed.
ReleaseTooling/Sources/FirebaseReleaser/InitializeRelease.swift:  private static func updateSwiftPackageVersion(path: URL, version: String) {
ReleaseTooling/Sources/Utils/ShellUtils.swift:/// when interacting with tools that can't be accessed directly in Swift (i.e. CocoaPods,
ReleaseTooling/Sources/ZipBuilder/CarthageUtils.swift:      if product == "FirebaseAnalyticsSwift" {
ReleaseTooling/Sources/ZipBuilder/CocoaPodUtils.swift:        // for all pods except Firebase and FirebaseCore. The Firebase Swift pods are not yet in the
ReleaseTooling/Sources/ZipBuilder/CocoaPodUtils.swift:           !pod.name.hasSuffix("Swift"),
ReleaseTooling/Sources/ZipBuilder/FrameworkBuilder.swift:    if framework == "FirebaseAppCheck" || framework.hasSuffix("Swift") {
ReleaseTooling/Sources/ZipBuilder/FrameworkBuilder.swift:                // BUILD_LIBRARY_FOR_DISTRIBUTION=YES is necessary for Swift libraries.
ReleaseTooling/Sources/ZipBuilder/FrameworkBuilder.swift:  /// Returns true to fail if building for Carthage and there are Swift modules.
ReleaseTooling/Sources/ZipBuilder/FrameworkBuilder.swift:    // In the case of a mixed language framework, not only are the Swift module
ReleaseTooling/Sources/ZipBuilder/FrameworkBuilder.swift:    // generated Swift header.
ReleaseTooling/Sources/ZipBuilder/FrameworkBuilder.swift:    if makeSwiftModuleMap(thinFrameworks: frameworks,
ReleaseTooling/Sources/ZipBuilder/FrameworkBuilder.swift:  /// Returns true if there are Swift modules.
ReleaseTooling/Sources/ZipBuilder/FrameworkBuilder.swift:  private func makeSwiftModuleMap(thinFrameworks: [URL],
ReleaseTooling/Sources/ZipBuilder/FrameworkBuilder.swift:            let destSwiftModuleDir = destModuleDir
ReleaseTooling/Sources/ZipBuilder/FrameworkBuilder.swift:                let destProjectDir = destSwiftModuleDir.appendingPathComponent("Project")
ReleaseTooling/Sources/ZipBuilder/FrameworkBuilder.swift:                    destSwiftModuleDir
ReleaseTooling/Sources/ZipBuilder/FrameworkBuilder.swift:                  fatalError("Could not copy Swift module file from \(fileURL) to " +
ReleaseTooling/Sources/ZipBuilder/FrameworkBuilder.swift:                    "\(destSwiftModuleDir): \(error)")
ReleaseTooling/Sources/ZipBuilder/FrameworkBuilder.swift:          // If this point is reached, the framework contains a Swift module,
ReleaseTooling/Sources/ZipBuilder/FrameworkBuilder.swift:          // so it's built from either Swift sources or Swift & C Family
ReleaseTooling/Sources/ZipBuilder/FrameworkBuilder.swift:          // Language sources. Frameworks built from only Swift sources will
ReleaseTooling/Sources/ZipBuilder/FrameworkBuilder.swift:          // and the Swift-generated Swift header. If the framework's `Headers`
ReleaseTooling/Sources/ZipBuilder/FrameworkBuilder.swift:            module \(frameworkName).Swift {
ReleaseTooling/Sources/ZipBuilder/FrameworkBuilder.swift:              header "\(frameworkName)-Swift.h"
ReleaseTooling/Sources/ZipBuilder/ZipBuilder.swift:      let (dir, frameworks) = try installAndCopyFrameworks(forPod: "FirebaseAnalyticsSwift",
ReleaseTooling/Sources/ZipBuilder/ZipBuilder.swift:    var metadataDeps = dependencyString(for: "FirebaseAnalyticsSwift",
ReleaseTooling/Sources/ZipBuilder/ZipBuilder.swift:          $0.key != "FirebaseAnalyticsSwift" &&
ReleaseTooling/Sources/ZipBuilder/ZipBuilder.swift:      let folder = pod.key == "GoogleSignInSwiftSupport" ? "GoogleSignIn" :
ReleaseTooling/Sources/ZipBuilder/ZipBuilder.swift:        pod.key.replacingOccurrences(of: "Swift", with: "")

It's not critical we remove them now, though.

[paulb777]

I believe most of these were addressed in #12080