Drop "substitute with upper bounds" mode for calls with mapped arguments

(we don't need it since we build constraint system for generic types).
Cleanup tests.

compiler/testData/diagnostics/tests/resolve/overloadConflicts/withVariance.kt

@@ -6,4 +6,4 @@ class A<T>
 fun <T1> A<T1>.foo() = X1
 fun <T2> A<out T2>.foo() = X2
 
-fun <T> A<out T>.test() = <!CANNOT_COMPLETE_RESOLVE!>foo<!>()
+fun <T> A<out T>.test() = <!CANNOT_COMPLETE_RESOLVE!>foo<!>() // TODO fix constraint system