tools: Remove feature-libelf-mmap feature detection

tools: Remove feature-libelf-mmap feature detection

It's trivial to handle missing ELF_C_MMAP_READ support in libelf the way that
objtool has solved it in
("774bec3fddcc objtool: Add fallback from ELF_C_READ_MMAP to ELF_C_READ").

So instead of having an entire feature detector for that, just do what objtool
does for perf and libbpf. And keep their Makefiles a bit simpler.

Signed-off-by: Andrii Nakryiko <[email protected]>
Signed-off-by: Alexei Starovoitov <[email protected]>
Link: https://lore.kernel.org/bpf/[email protected]