Remove Stale bot's configuration

We couldn't get stale bot to operate as we'd like (poke up N
older-then-X-period tickets a day) and therefore we're tearing it down.

We've chosen to keep the "stale" label, so tickets closed by the bot
may be found with that label.

.github/stale.yml

@@ -1,37 +0,0 @@
-# Default values: https://probot.github.io/apps/stale/#installation
-
-daysUntilStale: 1160 # ~3 yrs 2 months
-daysUntilClose: 30
-
-exemptLabels:
-  - C-tracking-issue      # keep tracking issues open
-  - C-feature-request     # keep feature requests open (at least for now)
-  - "Feature accepted"    # keep accepted features
-
-staleLabel: stale
-
-markComment: >
-  As there hasn't been any activity here in a while would someone (the author, a
-  team member, or any interested party) be able to summarise the current state,
-  perhaps making explicit:
-    * Is this still relevant?
-    * If so, what is blocking it?
-    * Is it known what could be done to help move this forward?
-
-  Thank you!
-
-
-  (The cargo team is currently evaluating the use of Stale bot, and using #6035
-  as the tracking issue to gather feedback.)
-
-
-  If you're reading this comment from the distant future, fear not if this
-  was closed automatically. If you believe it's still an issue please leave a
-  comment and a team member can reopen this issue. Opening a new issue is also
-  acceptable!
-
-closeComment: >
-  As I didn't see any updates in 30 days I'm going to close this.
-  Please see the previous comment for more information!
-
-limitPerRun: 1 # 1 per hour, so 24 per day