awscli: remove unnecessary override on python prompt_toolkit

This override to the old 1.x version of `prompt_toolkit` appears to be
unnecessary; removing it does not change the hash of `awscli`.

In a follow-up, we could likely remove the RSA override as well, if we're OK
with patching out the `setup.cfg` requirements. This dropped support for some
old modules, but appears to not break API compatibility otherwise:
https://github.com/sybrenstuvel/python-rsa/blob/master/CHANGELOG.md#version-40---released-2018-09-16

pkgs/tools/admin/awscli/default.nix

@@ -2,7 +2,6 @@
 , python3
 , groff
 , less
-, fetchpatch
 }:
 
 let
@@ -15,7 +14,6 @@ let
           sha256 = "25df4e10c263fb88b5ace923dd84bf9aa7f5019687b5e55382ffcdb8bede9db5";
         };
       });
-      prompt_toolkit = self.callPackage ../../../development/python-modules/prompt_toolkit/1.nix { };
     };
   };