Re-enable @available(macOS 11) test

rdar://66693249

Author: beccadax

test/attr/attr_availability_canonical_macos_version.swift

@@ -1,8 +1,5 @@
 // RUN: %swift -typecheck -verify -parse-stdlib -module-name Swift -target x86_64-apple-macosx11.0 %s
 
-// REQUIRES: rdar66693249
-
-
 @available(OSX, introduced: 10.5, deprecated: 10.8, obsoleted: 11.0,
               message: "you don't want to do that anyway")
 func obsoletedIn11() { }