It was added for Android extensions, but now another mechanism is used there
(PackageFragmentProviderExtension), and there were no other implementations of
ExternalDeclarationsProvider in the project
Writing source annotations enables incremental compilation for kapt2.
However they are not needed in bytecode, so we remove them when
copying classes.
# Conflicts:
# compiler/cli/src/org/jetbrains/kotlin/cli/jvm/K2JVMCompiler.kt
# compiler/frontend.java/src/org/jetbrains/kotlin/config/JVMConfigurationKeys.java