Revert "Fix FDE indexing while scan debug_info section."

This reverts commit r303847 as it introduces a number of regressions.
Investigation has showed that we are parsing the CIE entries in the
debug_frame section incorrectly -- we are parsing them the same way as
eh_frame, but the entries in debug_frame have a couple of extra entries
which have not been taken into account.

llvm-svn: 303854