py: Don't use gc or qstr mutex when the GIL is enabled.

There is no need since the GIL already makes gc and qstr operations
atomic.

py/gc.c

@@ -94,7 +94,7 @@
 #define FTB_CLEAR(block) do { MP_STATE_MEM(gc_finaliser_table_start)[(block) / BLOCKS_PER_FTB] &= (~(1 << ((block) & 7))); } while (0)
 #endif
 
-#if MICROPY_PY_THREAD
+#if MICROPY_PY_THREAD && !MICROPY_PY_THREAD_GIL
 #define GC_ENTER() mp_thread_mutex_lock(&MP_STATE_MEM(gc_mutex), 1)
 #define GC_EXIT() mp_thread_mutex_unlock(&MP_STATE_MEM(gc_mutex))
 #else