Remove stale generated 'genheaders' file

This bogus stale file was added in commit 1019712 ("riscv: add a
warning when physical memory address overflows").  It's the old location
for what is now 'security/selinux/genheaders'.

It looks like it got incorrectly committed back when that file was in
the old location, and then rebasing kept the bogus file alive.

Reported-by: Eric Biggers <ebiggers@kernel.org>
Link: https://lore.kernel.org/linux-riscv/20250201020003.GA77370@sol.localdomain/
Fixes: 1019712 ("riscv: add a  warning when physical memory address overflows")
Cc: Palmer Dabbelt <palmer@rivosinc.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>