test: remove unused compats #13748

Job	Run time
windows-latest jdk-17 unit tests 1 / 2	23m 46s
Gradle MacOS integration	21m 13s
windows-latest jdk-17 unit tests 2 / 2	22m 51s
Sbt integration	46m 20s
Maven integration	9m 37s
macOS-12 jdk-17 unit tests 1 / 2	38m 15s
macOS-12 jdk-17 unit tests 2 / 2	50m 36s
Gradle integration	9m 58s
Scala CLI integration	12m 26s
ubuntu-latest jdk-17 unit tests 1 / 2	19m 33s
Mill integration	30m 36s
ubuntu-latest jdk-17 unit tests 2 / 2	24m 7s
Bazel integration	10m 48s
LSP integration tests	33m 32s
Scala cross tests	34m 35s
Formatting	32s
Scalafix and docs	5m 36s
Sbt-metals/scripted jdk11	2m 57s
Scala javapc tests	1m 32s
Scala 2.11 cross tests	3m 47s
MiMa	38s
	6h 43m 15s

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