mail-parser: Remove invalid requirements.txt patch

Upstream modified requirements.txt and is no longer pinning
dependencies to exact versions. Instead, it provides version
bounds. Also, the ipaddress dependency is now limited already
in requirements.txt to Python versions < 3.3.

Removed all the patching since it generated an invalid
requirements.txt that caused the build to fail.

pkgs/development/python-modules/mail-parser/default.nix

@@ -14,16 +14,6 @@ buildPythonPackage rec {
 
   LC_ALL = "en_US.utf-8";
 
-  # remove version bounds
-  prePatch = ''
-    sed -i -e 's/==.*//g' requirements.txt
-  ''
-  # ipaddress is part of the standard library of Python 3.3+
-  + lib.optionalString (!pythonOlder "3.3") ''
-    substituteInPlace requirements.txt \
-      --replace "ipaddress" ""
-  '';
-
   nativeBuildInputs = [ glibcLocales ];
   propagatedBuildInputs = [ simplejson six ] ++ lib.optional (pythonOlder "3.3") ipaddress;