repos: remove my repo (ma27/nixexprs)

See nix-community#133 (comment)

Author: Ma27

repos.json

@@ -71,9 +71,6 @@
         "lschuermann": {
             "url": "https://github.com/lschuermann/nur-packages"
         },
-        "ma27": {
-            "url": "https://gitlab.com/Ma27/nixexprs"
-        },
         "makefu": {
             "file": "nur.nix",
             "url": "https://github.com/makefu/nur-packages"