RISC-V: Removed the v0.93 bitmanip ZBA/ZBB/ZBC instructions.

bfd/
    * elfxx-riscv.c (riscv_parse_prefixed_ext): Removed zb*.
gas/
    * config/tc-riscv.c (riscv_multi_subset_supports): Removed
    INSN_CLASS_ZB*.
    * testsuite/gas/riscv/bitmanip-insns-32.d: Removed.
    * testsuite/gas/riscv/bitmanip-insns-64.d: Removed.
    * testsuite/gas/riscv/bitmanip-insns.s: Removed.
include/
    * opcode/riscv-opc.h: Removed macros for zb* extensions.
    * opcode/riscv.h (riscv_insn_class): Removed INSN_CLASS_ZB*.
opcodes/
    * riscv-opc.c (MASK_RVB_IMM): Removed.
    (riscv_opcodes): Removed zb* instructions.
    (riscv_ext_version_table): Removed versions for zb*.