.guix-authorizations: Remove brettgilio's old key.

* .guix-authorizations: Remove key "DFC0 C7F7 9EE6 0CA7 AE55  5E19 6722
43C4 A03F 0EEE" (Brett Gilio).  See
<https://lists.gnu.org/archive/html/guix-devel/2020-06/msg00323.html>.

.guix-authorizations

@@ -35,8 +35,6 @@
    (name "biscuolo"))
   ("7988 3B9F 7D6A 4DBF 3719  0367 2506 A96C CF63 0B21"
    (name "boskovits"))
-  ("DFC0 C7F7 9EE6 0CA7 AE55  5E19 6722 43C4 A03F 0EEE"
-   (name "brettgilio"))
   (;; primary: "8929 BBC5 73CD 9206 3DDD 979D 3D36 CAA0 116F 0F99"
    "1C9B F005 1A1A 6A44 5257 599A A949 03A1 66A1 8FAE"
    (name "bricewge"))