Build: remove obsolete compiler arguments

These compiler arguments enable features which are enabled by default in
the current Kotlin anyway.

The only exception is in :compiler:cli which uses an old language
version.

kotlin-native/endorsedLibraries/kotlinx.cli/build.gradle

@@ -96,7 +96,7 @@ targetList.each { target ->
                 '-produce', 'library', '-module-name', moduleName,
                 '-Xmulti-platform', '-Xopt-in=kotlinx.cli.ExperimentalCli',
                 '-Xopt-in=kotlin.ExperimentalMultiplatform',
-                '-Xallow-result-return-type',  '-Werror', '-Xopt-in=kotlin.RequiresOptIn',
+                '-Werror', '-Xopt-in=kotlin.RequiresOptIn',
                 commonSrc.absolutePath,
                 "-Xcommon-sources=${commonSrc.absolutePath}",
                 nativeSrc]