removed obsolete variables

Former-commit-id: eab09eaea37b58b636b437df2833b4bd3cd9ea3e

lib/single-file/single-file-core.js

@@ -1246,10 +1246,6 @@ this.singlefile.lib.core = this.singlefile.lib.core || (() => {
 	const DATA_URI_PREFIX = "data:";
 	const ABOUT_BLANK_URI = "about:blank";
 	const EMPTY_DATA_URI = "data:base64,";
-	const REGEXP_AMP = /&/g;
-	const REGEXP_NBSP = /\u00a0/g;
-	const REGEXP_START_TAG = /</g;
-	const REGEXP_END_TAG = />/g;
 	const REGEXP_URL_HASH = /(#.+?)$/;
 	const PREFIX_DATA_URI_VND = "data:application/vnd.";
 	const SINGLE_FILE_VARIABLE_NAME_PREFIX = "--sf-img-";