Don't explicitly force utf strings into the __TEXT,__ustring

Don't explicitly force utf strings into the __TEXT,__ustring
by setting the section of the generated global.  This is an
optimization done by the code generator, and the code being
removed didn't handle the case when the string contained an
embedded nul (which the code generator does correctly
handle).  This is rdar://7589850

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@95003 91177308-0d34-0410-b5e6-96231b3b80d8