modpost: remove self-definitions of R_ARM_* macros

Commit f5983dab

 ("modpost: define more R_ARM_* for old
distributions") added self-definitions for the R_ARM_* macros to fix
build errors on CentOS 7.

RHEL/CentOS 7 were retired at the end of June.

Remove all the R_ARM_* definitions (except for R_ARM_THM_CALL), which
should be available in recent distributions.

glibc and musl added most of R_ARM_* macros in 2013. [1] [2]

[1]: https://sourceware.org/git/?p=glibc.git;a=commitdiff;h=08cbd996d33114ca50644d060fbe3a08260430fb
[2]: https://git.musl-libc.org/cgit/musl/commit/?id=268375c1c017c0bdefeed1a330811e433c4dfaef

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>