Fix auto-completion performance issue introduced with switch to static linkage of libSciLexer

The performance issue, which appears after switching to static linkage of libSciLexer, is due to th commit "Improve character case handling in RegEx" (#9707).
Removing "locale" call from "BoostRegexSearch::FindText()" solves auto-completion performance issue.

Fix #9975, close #10010

boostregex/BoostRegExSearch.cxx

@@ -306,11 +306,9 @@ Sci::Position BoostRegexSearch::FindText(Document* doc, Sci::Position startPosit
 			);
 		search._skip_windows_line_end_as_one_character = (sciSearchFlags & SCFIND_REGEXP_SKIPCRLFASONE) != 0;
 		
-		std::locale l = std::locale::global(std::locale(""));
 		Match match =
 			isUtf8 ? _utf8.FindText(search)
 			       : _ansi.FindText(search);
-		std::locale::global(l);
 
 		if (match.found())
 		{