Revert several changes related to llvm-symbolizer exiting non-zero on failure.

Seems users have enough different uses of the symbolizer where they
might have unknown binaries and offsets such that "best effort" behavior
is all that's expected of llvm-symbolizer - so even erroring on unknown
executables and out of bounds offsets might not be suitable.

This reverts commit 1de01997.
This reverts commit a7b209a6.
This reverts commit 338dd138.