Update and un-XFAIL doc_clang_module test

Author: slavapestov

test/SourceKit/DocSupport/doc_clang_module.swift

@@ -2,5 +2,3 @@
 // RUN: %sourcekitd-test -req=doc-info -module Foo -- -F %S/../Inputs/libIDE-mock-sdk \
 // RUN:         %mcp_opt %clang-importer-sdk | %sed_clean > %t.response
 // RUN: diff -u %s.response %t.response
-// XFAIL: *
-// TODO: re-enable or perhaps this is a bit too hard-coded a test?