No override check in FirClassUseSiteScope, fix nasty substitution bug

This fixes MPP override test
(see mppFakeOverride in FirMultiModuleResolveTestGenerated)

idea/testData/fir/multiModule/mppFakeOverrides/common/common.kt

@@ -3,8 +3,9 @@ expect open class A<T>() {
 }
 open class B : A<String>() {
     // Fake: override fun foo(arg: String) = super.foo(arg)
-    // Fake (JVM only) (?): override fun bar(arg: String): String = super.bar(arg)
+    // Fake (JVM only): override fun bar(arg: String): String = super.bar(arg)
 }
 open class C : B() {
-    open fun bar(arg: CharSequence): String = arg.toString()
+    open fun bar(arg: String): String = arg
+    open fun baz(arg: CharSequence): String = arg.toString()
 }

idea/testData/fir/multiModule/mppFakeOverrides/common/common.txt

@@ -12,8 +12,12 @@ FILE: common.kt
     public open class C : R|B| {
         public constructor(): super<R|B|>()
 
-        public open function bar(arg: R|kotlin/CharSequence|): R|kotlin/String| {
-            return@@@bar <Unresolved name: arg>#.<Unresolved name: toString>#()
+        public open function bar(arg: R|kotlin/String|): R|kotlin/String| {
+            return@@@bar <Unresolved name: arg>#
+        }
+
+        public open function baz(arg: R|kotlin/CharSequence|): R|kotlin/String| {
+            return@@@baz <Unresolved name: arg>#.<Unresolved name: toString>#()
         }
 
     }

idea/testData/fir/multiModule/mppFakeOverrides/jvm/jvm.kt

@@ -1,11 +1,12 @@
 actual open class A<T> {
     actual open fun foo(arg: T) {}
     open fun bar(arg: T): T = arg
+    open fun baz(arg: T): T = arg
 }
 class D : C() {
-    // Fake: override fun bar(arg: CharSequence): String = super.bar(arg)
     fun test() {
         foo("")
-        bar("")
+        bar("") // should be resolved to just C.bar
+        baz("") // ambiguity (we have C.bar with CharSequence argument and fake override of A.bar with String argument)
     }
 }

idea/testData/fir/multiModule/mppFakeOverrides/jvm/jvm.txt

@@ -9,13 +9,18 @@ FILE: jvm.kt
             return@@@bar <Unresolved name: arg>#
         }
 
+        public open function baz(arg: R|T|): R|T| {
+            return@@@baz <Unresolved name: arg>#
+        }
+
     }
     public final class D : R|C| {
         public constructor(): super<R|C|>()
 
         public final function test(): R|kotlin/Unit| {
             R|FakeOverride</A.foo: R|kotlin/Unit|>|(String())
-            <Ambiguity: bar, [/C.bar, /A.bar]>#(String())
+            R|/C.bar|(String())
+            <Ambiguity: baz, [/C.baz, /A.baz]>#(String())
         }
 
     }

idea/testData/fir/multiModule/overrideWithJava/jvm/B.kt

@@ -1,6 +1,6 @@
 class B : A() {
     override fun foo(): B = this
-    fun bar(): B = this // Ambiguity, no override here
+    fun bar(): B = this // Here we should have "missing override" but no ambiguity
 
     fun test() {
         foo()

idea/testData/fir/multiModule/overrideWithJava/jvm/B.txt

@@ -12,7 +12,7 @@ FILE: B.kt
 
         public final function test(): R|kotlin/Unit| {
             R|/B.foo|()
-            <Ambiguity: bar, [/B.bar, /A.bar]>#()
+            R|/B.bar|()
         }
 
     }