Added quickfix for NULLABLE_SUPERTYPE

idea/testData/quickfix/nullables/afterRemoveSupertypeNullable1.kt

@@ -0,0 +1,3 @@
+// "Remove '?'" "true"
+open class Foo() {}
+class Bar() : Foo<caret>() {}

idea/testData/quickfix/nullables/afterRemoveSupertypeNullable2.kt

@@ -0,0 +1,3 @@
+// "Remove '?'" "true"
+trait Foo {}
+class Bar : Foo<caret> {}

idea/testData/quickfix/nullables/beforeRemoveSupertypeNullable1.kt

@@ -0,0 +1,3 @@
+// "Remove '?'" "true"
+open class Foo() {}
+class Bar() : Foo?<caret>() {}

idea/testData/quickfix/nullables/beforeRemoveSupertypeNullable2.kt

@@ -0,0 +1,3 @@
+// "Remove '?'" "true"
+trait Foo {}
+class Bar : Foo?<caret> {}