s390: remove unused expoline to BC instructions

s390: remove unused expoline to BC instructions

This reverts commit 6deaa3bbca80 ("s390: extend expoline to BC
instructions"). Expolines to BC instructions were added to be utilized
by commit de5cb6eb514e ("s390: use expoline thunks in the BPF JIT"). But
corresponding code has been removed by commit e1cf4befa297 ("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>