[ELF][test] Use llvm-readelf's short option -r instead of -relocations and remove ignored --wide

Reviewers: ruiu, sfertile, espindola

Reviewed By: ruiu

Subscribers: jsji, emaste, nemanjai, arichardson, kbarton, llvm-commits

Differential Revision: https://reviews.llvm.org/D52124

llvm-svn: 343135