Have stripDebugInfo() also strip !llvm.loop annotations from all

instructions.

The !llvm.loop annotations consist of pointers into the debug info, so
when stripping the debug info (particularly important when it is
malformed!) !llvm.loop annotations need to be stripped as well, or
else the malformed debug info stays around.  This patch applies the
stripping to all instructions, not just terminator instructions.

rdar://73687049

Differential Revision: https://reviews.llvm.org/D96181