s390: remove unused expoline to BC instructions

s390: remove unused expoline to BC instructions

This reverts commit b39f7f80a314 ("s390: extend expoline to BC
instructions"). Expolines to BC instructions were added to be utilized
by commit 36758afe596b ("s390: use expoline thunks in the BPF JIT"). But
corresponding code has been removed by commit ed20d00e804e ("bpf, s390x:
remove ld_abs/ld_ind"). And compiler does not generate such expolines as
well.

Compared to regular expolines, expolines to BC instructions contain
displacement and all possible variations cannot be generated in advance,
making kpatch support more complicated. So, remove those to avoid
future usages.

Acked-by: Heiko Carstens <hca@linux.ibm.com>
Acked-by: Sumanth Korikkar <sumanthk@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>