Remove [objc_block] attribute from Swift type system.

We will handle Swift-function-to-ObjC-block bridging in SILGen as part of general Cocoa-to-Swift type bridging. Temporarily disable building swiftAppKit and tests that exercise block bridging until the new implementation lands.

Swift SVN r5090

lib/Parse/ParseDecl.cpp

@@ -190,18 +190,6 @@ bool Parser::parseAttribute(DeclAttributes &Attributes) {
     return false;
   }
     
-  // 'objc_block' attribute.
-  // FIXME: only permit this in type contexts.
-  case AttrName::objc_block: {
-    if (Attributes.Byref)
-      diagnose(Tok, diag::duplicate_attribute, Tok.getText());
-    consumeToken(tok::identifier);
-    
-    Attributes.ObjCBlock = true;
-    
-    return false;
-  }
-      
   // FIXME: Only valid on var and tuple elements, not on func's, typealias, etc.
   case AttrName::auto_closure: {
     SourceLoc TokLoc = Tok.getLoc();