x86: prune OBJ_MAYBE_... uses

With the removal of emulations, OBJ_MAYBE_... can no longer be defined.
Tidy code wherever they're used, which also includes the dropping of
most IS_ELF and uses and checks of OUTPUT_FLAVOR.

Where touching such constructs anyway, also drop TE_PEP checks when used
together with TE_PE ones (the former implies the latter).