vmlinux.lds.h: drop unused __vermagic

The reference to '__vermagic' is a relict from v2.5 times. And even
there it had a very short life time, from v2.5.59 (commit 1d411b80ee18
("Module Sanity Check") in the historic tree) to v2.5.69 (commit
67ac5b866bda ("[PATCH] complete modinfo section")).

Neither current kernels nor modules contain a '__vermagic' section any
more, so get rid of it.

Signed-off-by: Mathias Krause <minipli@googlemail.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Jessica Yu <jeyu@kernel.org>
Signed-off-by: Jessica Yu <jeyu@kernel.org>