K2: drop obsolete TODO about multiple WasExperimental

In certain situations like constructor calls, it's possible
to have different WasExperimental/SinceKotlin pairs associated
with one use-site, e.g. a constructor call is associated both
with a constructor declaration and a class declaration.
However, looks like it make no sense to handle this situation
in FirSinceKotlinHelpers, because FirOptInUsageBaseChecker already
handles them.

#KT-59825 Fixed

compiler/testData/diagnostics/testsWithStdLib/experimental/wasExperimentalCombined.fir.kt

@@ -0,0 +1,52 @@
+// API_VERSION: 1.8
+// !DIAGNOSTICS: -INVISIBLE_MEMBER -INVISIBLE_REFERENCE
+
+@RequiresOptIn
+@Retention(AnnotationRetention.BINARY)
+annotation class ClassMarker
+
+@RequiresOptIn
+@Retention(AnnotationRetention.BINARY)
+annotation class ConstructorMarker
+
+@RequiresOptIn
+@Retention(AnnotationRetention.BINARY)
+annotation class TypeAliasMarker
+
+@SinceKotlin("1.9")
+@WasExperimental(ClassMarker::class)
+class C {
+    @SinceKotlin("1.9")
+    @WasExperimental(ConstructorMarker::class)
+    constructor() {}
+}
+
+@SinceKotlin("1.9")
+@WasExperimental(TypeAliasMarker::class)
+typealias T = <!OPT_IN_USAGE_ERROR!>C<!>
+
+@ClassMarker
+fun test1() {
+    <!OPT_IN_USAGE_ERROR!>C<!>()
+}
+
+@ConstructorMarker
+fun test2() {
+    <!OPT_IN_USAGE_ERROR!>C<!>()
+}
+
+@ClassMarker
+@ConstructorMarker
+fun test3() {
+    C()
+}
+
+@ClassMarker
+fun test4(t: <!OPT_IN_USAGE_ERROR!>T<!>) {}
+
+@TypeAliasMarker
+fun test5(t: <!OPT_IN_USAGE_ERROR!>T<!>) {}
+
+@ClassMarker
+@TypeAliasMarker
+fun test6(t: T) {}

compiler/testData/diagnostics/testsWithStdLib/experimental/wasExperimentalCombined.kt

@@ -0,0 +1,52 @@
+// API_VERSION: 1.8
+// !DIAGNOSTICS: -INVISIBLE_MEMBER -INVISIBLE_REFERENCE
+
+@RequiresOptIn
+@Retention(AnnotationRetention.BINARY)
+annotation class ClassMarker
+
+@RequiresOptIn
+@Retention(AnnotationRetention.BINARY)
+annotation class ConstructorMarker
+
+@RequiresOptIn
+@Retention(AnnotationRetention.BINARY)
+annotation class TypeAliasMarker
+
+@SinceKotlin("1.9")
+@WasExperimental(ClassMarker::class)
+class C {
+    @SinceKotlin("1.9")
+    @WasExperimental(ConstructorMarker::class)
+    constructor() {}
+}
+
+@SinceKotlin("1.9")
+@WasExperimental(TypeAliasMarker::class)
+typealias T = <!OPT_IN_USAGE_ERROR!>C<!>
+
+@ClassMarker
+fun test1() {
+    <!UNRESOLVED_REFERENCE!>C<!>()
+}
+
+@ConstructorMarker
+fun test2() {
+    <!OPT_IN_USAGE_ERROR!>C<!>()
+}
+
+@ClassMarker
+@ConstructorMarker
+fun test3() {
+    C()
+}
+
+@ClassMarker
+fun test4(t: <!OPT_IN_USAGE_ERROR!>T<!>) {}
+
+@TypeAliasMarker
+fun test5(t: <!OPT_IN_USAGE_ERROR!>T<!>) {}
+
+@ClassMarker
+@TypeAliasMarker
+fun test6(t: T) {}