Tests: Remove REQUIRES: executable_test from ASTGen/attrs.swift.

It is not an executable test.

Resolves rdar://159025990.

Author: tshortli

test/ASTGen/attrs.swift

@@ -35,7 +35,6 @@
 // RUN:   -enable-experimental-move-only
 
 // REQUIRES: concurrency
-// REQUIRES: executable_test
 // REQUIRES: swift_swift_parser
 // REQUIRES: swift_feature_ParserASTGen
 // REQUIRES: swift_feature_Extern