[lld] Remove 2>&1 from --trace-symbol tests

The tracing goes to stdout so this is not needed.

Also remove the "not" from the final check in ELF/trace-symbols.s.
According the comment the check is that we don't crash, so we should
be checking for success here. Previously this step is error'ing with
undefined symbols because it didn't include all the needed objects.

Differential Revision: https://reviews.llvm.org/D61928

llvm-svn: 360794