Special2 opcode have been removed from the Release 6.
Add a single decodetree entry for all the opcode class,
triggering Reserved Instruction if ever used.
Remove unreachable check_insn_opc_removed() call.
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20201208203704.243704-7-f4bug@amsat.org>