Remove unnecessary frontend option

Author: DougGregor

include/swift/Option/Options.td

@@ -635,11 +635,6 @@ def enable_experimental_cxx_interop_in_clang_header :
   Flags<[FrontendOption, NoDriverOption, HelpHidden]>,
   HelpText<"Enable experimental Swift to C++ interop code generation in generated Clang header">;
 
-def enable_experimental_swift_parser :
-  Flag<["-"], "enable-experimental-swift-parser">,
-  Flags<[FrontendOption, HelpHidden, ModuleInterfaceOption]>,
-  HelpText<"Enable the new and expiremental Swift parser + AST generation.">;
-
 def experimental_cxx_stdlib :
   Separate<["-"], "experimental-cxx-stdlib">,
   Flags<[HelpHidden]>,