Remove -disable-implicit-distributed-module-import.

Distributed is never implicitly imported.

Author: rxwei

include/swift/Option/FrontendOptions.td

@@ -422,10 +422,6 @@ def disable_implicit_concurrency_module_import : Flag<["-"],
   "disable-implicit-concurrency-module-import">,
   HelpText<"Disable the implicit import of the _Concurrency module.">;
 
-def disable_implicit_distributed_module_import : Flag<["-"],
-  "disable-implicit-distributed-module-import">,
-  HelpText<"Disable the implicit import of the Distributed module.">;
-
 def disable_implicit_string_processing_module_import : Flag<["-"],
   "disable-implicit-string-processing-module-import">,
   HelpText<"Disable the implicit import of the _StringProcessing module.">;

stdlib/cmake/modules/AddSwiftStdlib.cmake

@@ -1754,12 +1754,6 @@ function(add_swift_target_library name)
   # Turn off implicit import of _Concurrency when building libraries
   list(APPEND SWIFTLIB_SWIFT_COMPILE_FLAGS "-Xfrontend;-disable-implicit-concurrency-module-import")
 
-  # Turn off implicit import of Distributed when building libraries
-  if(SWIFT_ENABLE_EXPERIMENTAL_DISTRIBUTED)
-    list(APPEND SWIFTLIB_SWIFT_COMPILE_FLAGS
-                      "-Xfrontend;-disable-implicit-distributed-module-import")
-  endif()
-
   # Turn off implicit import of _StringProcessing when building libraries
   if(SWIFT_ENABLE_EXPERIMENTAL_STRING_PROCESSING)
     list(APPEND SWIFTLIB_SWIFT_COMPILE_FLAGS