unix: Enable MICROPY_PY_STR_BYTES_CMP_WARN.

Also, fix a warning text (remove "duplicate" BytesWarning).

py/obj.c

@@ -199,7 +199,7 @@ bool mp_obj_equal(mp_obj_t o1, mp_obj_t o2) {
     str_cmp_err:
         #if MICROPY_PY_STR_BYTES_CMP_WARN
         if (MP_OBJ_IS_TYPE(o1, &mp_type_bytes) || MP_OBJ_IS_TYPE(o2, &mp_type_bytes)) {
-            mp_warning("BytesWarning: Comparison between bytes and str");
+            mp_warning("Comparison between bytes and str");
         }
         #endif
         return false;

unix/mpconfigport.h

@@ -138,6 +138,7 @@
 // names in exception messages (may require more RAM).
 #define MICROPY_ERROR_REPORTING     (MICROPY_ERROR_REPORTING_DETAILED)
 #define MICROPY_WARNINGS            (1)
+#define MICROPY_PY_STR_BYTES_CMP_WARN (1)
 
 // Define to 1 to use undertested inefficient GC helper implementation
 // (if more efficient arch-specific one is not available).