Sema: Remove useless MSStructPragmaOn update in Sema::~Sema

No functional change, this code was just superfluous.


git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@201099 91177308-0d34-0410-b5e6-96231b3b80d8
PR18777: This PR is already fixed; add regtest.


git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@201100 91177308-0d34-0410-b5e6-96231b3b80d8