Revert "[Conformance] Always downgrade redundant conformances to marker protocols to"

This reverts commit 5eb16ad.

Author: hborla

lib/Sema/TypeCheckProtocol.cpp

@@ -6390,7 +6390,7 @@ void TypeChecker::checkConformancesInContext(IterableDeclContext *idc) {
     }
 
     if ((existingModule != dc->getParentModule() && conformanceInOrigModule) ||
-        diag.Protocol->isMarkerProtocol()) {
+        isSendable) {
       // Warn about the conformance.
       if (isSendable && SendableConformance &&
           isa<InheritedProtocolConformance>(SendableConformance)) {

test/decl/protocol/conforms/redundant_conformance.swift

@@ -86,10 +86,3 @@ class Class3 {
 class SomeMockClass: Class3.ProviderThree { // okay
   var someInt: Int = 5
 }
-
-
-class ImplicitCopyable {}
-
-class InheritImplicitCopyable: ImplicitCopyable, Copyable {}
-// expected-warning@-1 {{redundant conformance of 'InheritImplicitCopyable' to protocol 'Copyable'}}
-// expected-note@-2 {{'InheritImplicitCopyable' inherits conformance to protocol 'Copyable' from superclass here}}