[ARM] Revert r297443 and r297820.

The glueless lowering of addc/adde in Thumb1 has known serious
miscompiles (see https://reviews.llvm.org/D31081), and r297820
causes an infinite loop for certain constructs.  It's not
clear when they will be fixed, so let's just take them out
of the tree for now.

(I resolved a small conflict with r297453.)

llvm-svn: 298328