Revert "Suppress duplicated-branches compiler warning in mbfilter"

This reverts commit 6b3757e760342f63e80eff9d228d4860fd7a0389.

Author: Girgias

ext/mbstring/libmbfl/mbfl/mbfilter.c

@@ -1893,17 +1893,13 @@ mime_header_encoder_new(
 		return NULL;
 	}
 
-	/* Value of the constants are identical */
-#pragma GCC diagnostic push
-#pragma GCC diagnostic ignored "-Wduplicated-branches"
 	if (transenc->no_encoding == mbfl_no_encoding_qprint) {
 		pe->encod_filter->status |= MBFL_QPRINT_STS_MIME_HEADER;
 		pe->encod_filter_backup->status |= MBFL_QPRINT_STS_MIME_HEADER;
 	} else {
 		pe->encod_filter->status |= MBFL_BASE64_STS_MIME_HEADER;
 		pe->encod_filter_backup->status |= MBFL_BASE64_STS_MIME_HEADER;
 	}
-#pragma GCC diagnostic pop
 
 	return pe;
 }