Eliminate DistributedOnly flag on attributes.

Distributed actors are enabled by default, so we don't need this flag
any more.

Author: DougGregor

include/swift/AST/Attr.def

@@ -657,7 +657,6 @@ SIMPLE_DECL_ATTR(_inheritActorContext, InheritActorContext,
 
 CONTEXTUAL_SIMPLE_DECL_ATTR(distributed, DistributedActor,
   DeclModifier | OnClass | OnFunc | OnVar |
-  DistributedOnly |
   ABIBreakingToAdd | ABIBreakingToRemove |
   APIBreakingToAdd | APIBreakingToRemove,
   118)
@@ -723,7 +722,6 @@ DECL_ATTR(_backDeploy, BackDeploy,
 
 CONTEXTUAL_SIMPLE_DECL_ATTR(_local, KnownToBeLocal,
   DeclModifier | OnFunc | OnParam | OnVar |
-  DistributedOnly |
   ABIBreakingToAdd | ABIBreakingToRemove |
   APIBreakingToAdd | APIBreakingToRemove,
   130)

include/swift/AST/Attr.h

@@ -287,11 +287,8 @@ class DeclAttribute : public AttributeBase {
     /// Whether this attribute is only valid when concurrency is enabled.
     ConcurrencyOnly = 1ull << (unsigned(DeclKindIndex::Last_Decl) + 16),
 
-    /// Whether this attribute is only valid when distributed is enabled.
-    DistributedOnly = 1ull << (unsigned(DeclKindIndex::Last_Decl) + 17),
-
     /// Whether this attribute is valid on additional decls in ClangImporter.
-    OnAnyClangDecl = 1ull << (unsigned(DeclKindIndex::Last_Decl) + 18),
+    OnAnyClangDecl = 1ull << (unsigned(DeclKindIndex::Last_Decl) + 17),
   };
 
   LLVM_READNONE
@@ -386,10 +383,6 @@ class DeclAttribute : public AttributeBase {
     return getOptions(DK) & ConcurrencyOnly;
   }
 
-  static bool isDistributedOnly(DeclAttrKind DK) {
-    return getOptions(DK) & DistributedOnly;
-  }
-
   static bool isUserInaccessible(DeclAttrKind DK) {
     return getOptions(DK) & UserInaccessible;
   }