Do not require --enable-test-discovery anymore on Linux (#3579)

We have made the flag default a while ago, so we can assume that it'll be passed as default.

Author: neonichu

IntegrationTests/Tests/LinuxMain.swift

@@ -48,7 +48,7 @@ services:
 
   test:
     <<: *common
-    command: /bin/bash -cl "swift test --enable-test-discovery --parallel"
+    command: /bin/bash -cl "swift test --parallel"
 
   bootstrap-clean:
     <<: *common

Tests/LinuxMain.swift

@@ -335,7 +335,6 @@ def test(args):
     note("Testing")
     parse_test_args(args)
     cmd = [os.path.join(args.bin_dir, "swift-test")]
-    cmd.append("--enable-test-discovery")
     if args.parallel:
         cmd.append("--parallel")
     for arg in args.filter:

Utilities/Docker/docker-compose.yaml

@@ -15,9 +15,9 @@ set -x
 # Perform package update in order to get the latest commits for the dependencies.
 swift package update
 swift build -c $CONFIGURATION
-swift test -c $CONFIGURATION --parallel --enable-test-discovery
+swift test -c $CONFIGURATION --parallel
 
 # Run the integration tests with just built SwiftPM.
 export SWIFTPM_BIN_DIR=$(swift build -c $CONFIGURATION --show-bin-path)
 cd IntegrationTests
-$SWIFTPM_BIN_DIR/swift-test --parallel --enable-test-discovery
+$SWIFTPM_BIN_DIR/swift-test --parallel