many: use Mu::Regex instead of std::regex

The former is PCRE-compatible, and faster than std::regex.

lib/utils/mu-utils.hh

@@ -33,7 +33,6 @@
 #include <type_traits>
 #include <algorithm>
 #include <numeric>
-#include <regex>
 
 #include "mu-utils-format.hh"
 #include "mu-option.hh"
@@ -97,16 +96,6 @@ std::vector<std::string> split(const std::string& str, const std::string& sepa);
  */
 std::vector<std::string> split(const std::string& str, char sepa);
 
-/**
- * Split a string in parts
- *
- * @param str a string
- * @param sepa the separator regex
- *
- * @return the parts.
- */
-std::vector<std::string> split(const std::string& str, const std::regex& sepa_rx);
-
 /**
  * Join the strings in svec into a string, separated by sepa
  *
@@ -173,8 +162,6 @@ bool locale_workaround();
  */
 bool timezone_available(const std::string& tz);
 
-
-
 /**
  * Well-known runtime paths
  *