Revert r291903 and r291898. Reason: they break check-lld on the bots.

Summary:
Revert [ARM] Fix ubig32_t read in ARMAttributeParser

Now using support functions to read data instead of trying to
perform casts.
===========================================================

Revert [ARM] Enable objdump to construct triple for ARM

Now that The ARMAttributeParser has been moved into the library,
it has been modified so that it can parse the attributes without
printing them and stores them in a map. ELFObjectFile now queries
the attributes to fill out the architecture details of a provided
triple for 'arm' and 'thumb' targets. llvm-objdump uses this new
functionality.

Subscribers: llvm-commits, samparker, aemerson, mgorny

Differential Revision: https://reviews.llvm.org/D28683

llvm-svn: 291911