github: remove CODEOWNERS file

Since it was added, we never maintained the file leading to decay in the
set of "actual" code owners. In practice, the current set up ends up
assign most reviews to 2 or so active contributors. I think the idea
itself is sound, but the current implementation leads to certain
reviewers being over-assigned PRs, which at times causes those PRs to
stagnate since pretty much every PR gets assigned to the same set of
people.

.github/CODEOWNERS

@@ -1,79 +0,0 @@
-aezeed/* @roasbeef @cfromknecht
-
-autopilot/* @halseth @roasbeef
-
-brontide/* @roasbeef @cfromknecht
-
-buffer/* @cfromknecht
-
-build/* @cfromknecht
-
-chainntnfs/* @halseth @wpaulino
-
-chanbackup/* @roasbeef
-
-channeldb/channel.go @roasbeef
-
-channeldb/forwarding_log.go @roasbeef
-
-channeldb/graph.go @roasbeef @halseth
-
-channeldb/invoices.go @roasbeef @joostjager
-
-channeldb/payment_control.go @halseth @joostjager
-
-channeldb/payments.go @halseth @joostjager
-
-channeldb/reject_cache.go @cfromknecht
-
-channelnotifier/* @valentinewallace
-
-contractcourt/* @roasbeef @joostjager
-
-discovery/* @halseth @wpaulino
-
-htlcswitch/* @roasbeef @cfromknecht
-
-input/* @joostjager @roasbeef
-
-keychain/* @roasbeef
-
-lnwallet/* @roasbeef @halseth
-
-macaroons/* @roasbeef
-
-monitoring/* @valentinewallace
-
-nat/* @wpaulino
-
-pool/* @cfromknecht
-
-queue/* @cfromknecht
-
-routing/* @joostjager @roasbeef
-
-sweep/* @joostjager
-
-tor/* @wpaulino
-
-walletunlocker/* @roasbeef
-
-watchtower/* @cfromknecht @roasbeef
-
-zpay32/* @halseth @roasbeef
-
-breacharbiter.go @cfromknecht @roasbeef
-
-chanrestore.go @roasbeef
-
-fundingmanager.go @halseth @roasbeef
-
-nursery_store.go @cfromknecht
-
-peer.go @cfromknecht @roasbeef
-
-pilot.go @halseth @roasbeef
-
-server.go @cfromknecht @roasbeef
-
-utxonursery.go @cfromknecht @roasbeef