The original idea behind this change was to remove a use of the
deprecated CancelRequest method. Simply removing it would've been an
option, but I couldn't resist and did a bit of a refactoring instead.

All remote sealing code was contained in a single giant function. Remote
sealing is now extracted into its own object, remoteSealer.

deps: update fastcache to 1.5.3

core/rawdb: fix reinit regression caused by the hash check PR

* core: fix staticcheck warnings

* fix goimports

* p2p/discover: slow down lookups on empty table

* p2p/discover: wake from slowdown sleep when table is closed

* accounts/keystore: fix staticcheck warnings

* review feedback

* rlp: fix staticcheck warnings

* rlp: fix ExampleDecode test

cmd/geth: remove network id from version cmd

It was reflective only of the Default setting,
and not chain aware.

Numbers were already allowed when creating labels, just not when
referencing them.

* p2p/discv5: add deprecation warning and remove unused code

* p2p/discv5: remove unused variables

Also remove dependency on gopkg.in/check.v1 in tests.

* accounts/abi: fix staticcheck warnings

* accounts/abi: restore unused field for test

build: skip go clean on PPA, messes with the module trick

build: pull in ci.go dependencies for the PPA builder