string_util: Remove ThousandSeparate()

This is currently unused and doesn't really provide much value to keep
around either.

src/common/string_util.h

@@ -26,20 +26,6 @@ std::string StringFromBuffer(const std::vector<u8>& data);
 std::string StripSpaces(const std::string& s);
 std::string StripQuotes(const std::string& s);
 
-// Thousand separator. Turns 12345678 into 12,345,678
-template <typename I>
-std::string ThousandSeparate(I value, int spaces = 0) {
-    std::ostringstream oss;
-
-// std::locale("") seems to be broken on many platforms
-#if defined _WIN32 || (defined __linux__ && !defined __clang__)
-    oss.imbue(std::locale(""));
-#endif
-    oss << std::setw(spaces) << value;
-
-    return oss.str();
-}
-
 std::string StringFromBool(bool value);
 
 bool TryParse(const std::string& str, bool* output);