[llvm-objdump] -r: print non-SHF_ALLOC relocations for non-ET_REL files

ET_EXEC and ET_DYN files may contain non-SHF_ALLOC relocation sections
(e.g. ld --emit-relocs). Match GNU objdump by dumping them.

* Remove Object/dynamic-reloc.test. Replace it with a -r RUN line in dynamic-relocs.test
* Update relocations-in-nonreloc.test to set sh_link/sh_info. GNU
  objdump seems to ignore a SHT_REL/SHT_RELA section not linking to SHT_SYMTAB.
  The test did not test what it intended to test.

Fix https://github.com/llvm/llvm-project/issues/41246

Reviewed By: jhenderson

Differential Revision: https://reviews.llvm.org/D128959