lib: Don't check MIDELEG and MEDELEG at end of delegate_traps()

The MIDELEG and MEDELEG CSR checks at end of delegate_traps() were
added for initial bring-up on SiFive Unleashed and QEMU. These
checks are not required any more and in-future these checks can
cause failures because some of the MIDELEG/MEDELEG bits will be
hard-wired to 0 or 1.

For related discussion, refer github issue:
https://github.com/riscv/opensbi/issues/157



Signed-off-by: Anup Patel <anup.patel@wdc.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Atish Patra <atish.patra@wdc.com>