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

analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/diagnostic/compiler/based/DiagnosticCompilerTestFE10TestdataTestGenerated.java

@@ -43118,6 +43118,12 @@ public class DiagnosticCompilerTestFE10TestdataTestGenerated extends AbstractDia
                 runTest("compiler/testData/diagnostics/testsWithStdLib/experimental/wasExperimental.kt");
             }
 
+            @Test
+            @TestMetadata("wasExperimentalCombined.kt")
+            public void testWasExperimentalCombined() throws Exception {
+                runTest("compiler/testData/diagnostics/testsWithStdLib/experimental/wasExperimentalCombined.kt");
+            }
+
             @Test
             @TestMetadata("wrongTargetsWithoutExplicitTarget.kt")
             public void testWrongTargetsWithoutExplicitTarget() throws Exception {

analysis/low-level-api-fir/tests/org/jetbrains/kotlin/analysis/low/level/api/fir/diagnostic/compiler/based/LLFirPreresolvedReversedDiagnosticCompilerFE10TestDataTestGenerated.java

@@ -43118,6 +43118,12 @@ public class LLFirPreresolvedReversedDiagnosticCompilerFE10TestDataTestGenerated
                 runTest("compiler/testData/diagnostics/testsWithStdLib/experimental/wasExperimental.kt");
             }
 
+            @Test
+            @TestMetadata("wasExperimentalCombined.kt")
+            public void testWasExperimentalCombined() throws Exception {
+                runTest("compiler/testData/diagnostics/testsWithStdLib/experimental/wasExperimentalCombined.kt");
+            }
+
             @Test
             @TestMetadata("wrongTargetsWithoutExplicitTarget.kt")
             public void testWrongTargetsWithoutExplicitTarget() throws Exception {