[clang-format] Simplify raw string regex. NFC.

[curdeius]

Summary

Introduced in https://reviews.llvm.org/D115168.

clang/lib/Format/Format.cpp

tooling::Replacements sortCppIncludes(const FormatStyle &Style, StringRef Code,
   //
   // FIXME: Do some validation, e.g. edit distance of the base name, to fix
   // cases where the first #include is unlikely to be the main header.
   tooling::IncludeCategoryManager Categories(Style.IncludeStyle, FileName);
   bool FirstIncludeBlock = true;
   bool MainIncludeFound = false;
   bool FormattingOff = false;
 
+  // '[' must be the first and '-' the last character inside [...].
   llvm::Regex RawStringRegex(
-      "R\"(([\\[A-Za-z0-9_{}#<>%:;.?*+/^&\\$|~!=,'\\-]|])*)\\(");
+      "R\"([][A-Za-z0-9_{}#<>%:;.?*+/^&\\$|~!=,'-]*)\\(");
   SmallVector<StringRef, 2> RawStringMatches;
   std::string RawStringTermination = ")\"";
 
   for (;;) {
     auto Pos = Code.find('\n', SearchFrom);
     StringRef Line =
         Code.substr(Prev, (Pos != StringRef::npos ? Pos : Code.size()) - Prev);