Remove explicit "" handling in ConfigParser

Because `""` is a special case of `"..."` as parsed since gitpython-developers#2035.

Author: EliahKagan

git/config.py

@@ -501,9 +501,6 @@ def string_decode(v: str) -> str:
                         if pos != -1 and optval[pos - 1].isspace():
                             optval = optval[:pos]
                     optval = optval.strip()
-                    if optval == '""':
-                        optval = ""
-                    # END handle empty string
                     optname = self.optionxform(optname.rstrip())
                     if len(optval) > 1 and optval[0] == '"' and optval[-1] != '"':
                         is_multi_line = True