kldxref: Don't warn and skip file if no relocations are found

[jrtc27]

Summary

This case is hit for the kernel itself on riscv64, and did not used to
be checked. Since the code here can already handle missing Elf_Rel
and/or Elf_Rela just delete the check.

Fixes: 0299afdff145 ("kldxref: Make use of libelf to be a portable cross tool")
MFC after: 1 week

[imp]

Seems legit