Perf: don't run the regex replace unless the selectorText contains a colon (#1280)

* Perf: don't run the regex replace unless the selectorText contains a colon (rules generally contain colons)

* Need to check type before querying selectorText property - also good as it means we only try to fix colons at the leaf level
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Authored-by: eoghan murray <eoghan@getthere.ie>

packages/rrweb-snapshot/src/snapshot.ts

@@ -22,7 +22,6 @@ import {
   stringifyStylesheet,
   getInputType,
   toLowerCase,
-  validateStringifiedCssRule,
 } from './utils';
 
 let _id = 1;