Revert r192758 (and r192759), "MC: Better handling of tricky symbol and section names"

GNU AS didn't like quotes in symbol names.

    Error: junk at end of line, first unrecognized character is `"'

        .def "@feat.00";
        "@feat.00" = 1

Reproduced on Cygwin's 2.23.52.20130309 and mingw32's 2.20.1.20100303.

llvm-svn: 192775