Revert "Patch by Ray Donnelly to print register names instead of numbers."

This reverts commit r206683.

The code was confusing SEH register numbers with DWARF register numbers.
The test case it was committed with was obviously incorrect.  The
disassembler was roundtripping '.seh_pushreg %rsi' as '.seh_pushreg
%rbp', and other exciting things.

Noticed by Vadim Chugunov.

llvm-svn: 210574