src: convert hex2bin() into a regular function

No need to write hex2bin() as a function template because it's only
called with a char parameter.

Signed-off-by: Darshan Sen <raisinten@gmail.com>

PR-URL: nodejs#42321
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

src/node_url.cc

@@ -222,8 +222,7 @@ void AppendOrEscape(std::string* str,
     *str += ch;
 }
 
-template <typename T>
-unsigned hex2bin(const T ch) {
+unsigned hex2bin(const char ch) {
   if (ch >= '0' && ch <= '9')
     return ch - '0';
   if (ch >= 'A' && ch <= 'F')