accel/tcg: Remove mmap_lock/unlock from watchpoint.c

The mmap_lock is user-only, whereas watchpoint.c
is only compiled for system mode.

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

accel/tcg/watchpoint.c

@@ -124,17 +124,14 @@ void cpu_check_watchpoint(CPUState *cpu, vaddr addr, vaddr len,
             }
             cpu->watchpoint_hit = wp;
 
-            mmap_lock();
             /* This call also restores vCPU state */
             tb_check_watchpoint(cpu, ra);
             if (wp->flags & BP_STOP_BEFORE_ACCESS) {
                 cpu->exception_index = EXCP_DEBUG;
-                mmap_unlock();
                 cpu_loop_exit(cpu);
             } else {
                 /* Force execution of one insn next time.  */
                 cpu->cflags_next_tb = 1 | CF_NOIRQ | curr_cflags(cpu);
-                mmap_unlock();
                 cpu_loop_exit_noexc(cpu);
             }
         } else {