[lld-macho][nfc] Remove unnecessary -pie flags in tests

D101513 means that we no longer need to specify `-pie` in most of our
test RUN commands. Let's clean up the unused flags so as not to confuse
future test writers.

Reviewed By: #lld-macho, oontvoo, MaskRay

Differential Revision: https://reviews.llvm.org/D113114