this hasn't worked in...years (#4585)

diff --git a/.mention-bot b/.mention-bot
deleted file mode 100644
index a05018e..0000000
--- a/.mention-bot
+++ /dev/null
@@ -1,3 +0,0 @@
-{
-    "userBlacklist": ["dreid", "exarkun", "dstufft"]
-}