Remove double tests of tests/pos (#18683)

We should not tests all `tests/pos` files twice with another set of
flags. Furthermore, in all our tests the result of adding the flags is
not checked in any meaningful way. The only tests for this flag
(tests/neg-custom-args/fatal-warnings/i17612b/i17612b.scala) does add
the flag explicitly and checks the result already.

See
46f2db6

compiler/test/dotty/tools/dotc/CompilationTests.scala

@@ -34,7 +34,6 @@ class CompilationTests {
       compileFilesInDir("tests/pos", defaultOptions.and("-Ysafe-init")),
       compileFilesInDir("tests/pos-deep-subtype", allowDeepSubtypes),
       compileFilesInDir("tests/pos-special/sourcepath/outer", defaultOptions.and("-sourcepath", "tests/pos-special/sourcepath")),
-      compileFilesInDir("tests/pos", defaultOptions.and("-Xlint:private-shadow", "-Xlint:type-parameter-shadow")),
       compileFile("tests/pos-special/sourcepath/outer/nested/Test4.scala", defaultOptions.and("-sourcepath", "tests/pos-special/sourcepath")),
       compileFilesInDir("tests/pos-scala2", defaultOptions.and("-source", "3.0-migration")),
       compileFilesInDir("tests/pos-custom-args/captures", defaultOptions.and("-language:experimental.captureChecking")),