stylelintrc.json: Remove unused pattern

This was recently added in I276325d to allow utilizing the
exception in CSS file but subsequent iterations of the patch
voided the need for this exception, but this file was not updated.

Change-Id: I67cbebe6ba541ca0a3b1ff4a731d949a1d88c994

.stylelintrc.json

@@ -1,7 +1,7 @@
 {
 	"extends": "stylelint-config-wikimedia",
 	"rules": {
-		"selector-class-pattern": "^((mw|oo-ui)-|(wikitable|(toc(|toggle|hidden))|client-(no)?js)|sitedir-(ltr|rtl)$)",
+		"selector-class-pattern": "^((mw|oo-ui)-|(wikitable|(toc(|toggle|hidden))|client-(no)?js)$)",
 		"no-descending-specificity": null,
 		"selector-max-id": null
 	}