Fir2Ir: simplify getCachedIrTypeParameter

I could not figure out the reason for the special case in that function.
Tests do not show anything useful.

native/native.tests/tests-gen/org/jetbrains/kotlin/konan/blackboxtest/NativeCodegenBoxTestGenerated.java

@@ -5515,6 +5515,12 @@ public class NativeCodegenBoxTestGenerated extends AbstractNativeCodegenBoxTest
                 runTest("compiler/testData/codegen/box/compileKotlinAgainstKotlin/expectClassActualTypeAlias.kt");
             }
 
+            @Test
+            @TestMetadata("genericSetter.kt")
+            public void testGenericSetter() throws Exception {
+                runTest("compiler/testData/codegen/box/compileKotlinAgainstKotlin/genericSetter.kt");
+            }
+
             @Test
             @TestMetadata("innerClassConstructor.kt")
             public void testInnerClassConstructor() throws Exception {