[FIR] Fix incorrect inference of return type of anonymous functions

Also remove incorrect subtype check checkers

Test unsafeVarianceInAliasedFunctionalType.kt started to fail because
  of KT-54894. This bug existed before, changes from this commit just
  unhided it (previously it was hidden because incorrect subtype check
  in `isSubtypeForTypeMismatch` which is used by FirFunctionReturnTypeMismatchChecker

compiler/testData/diagnostics/tests/generics/projectionsScope/unsafeVarianceInAliasedFunctionalType.fir.kt

@@ -0,0 +1,11 @@
+class Foo<out T>(val baz: Baz<T>)
+
+class Bar {
+    val foo: Foo<*> = TODO()
+
+    fun <T> bar(): Baz<T> {
+        return <!RETURN_TYPE_MISMATCH!>foo.baz<!>
+    }
+}
+
+typealias Baz<T> = (@UnsafeVariance T) -> Unit

compiler/testData/diagnostics/tests/generics/projectionsScope/unsafeVarianceInAliasedFunctionalType.kt

@@ -1,4 +1,3 @@
-// FIR_IDENTICAL
 class Foo<out T>(val baz: Baz<T>)
 
 class Bar {