Remove Polkadot & Kusama native runtime (#1304)

This pull request removes the Polkadot and Kusama native runtime from
the polkadot node. This brings some implications with it:

There are no more kusama/polkadot-dev chain specs available. We will
need to write some tooling in the fellowship repo to provide them
easily.

The try-runtime job for polkadot & kusama is not available anymore as we
don't have the dev chain specs anymore.

Certain benchmarking commands will also not work until we migrate them
to use a runtime api.

Some crates in utils are still depending on the polkadot/kusama native
runtime that will also need to be fixed.

Port of: https://github.com/paritytech/polkadot/pull/7467

.gitlab/pipeline/short-benchmarks.yml

@@ -5,7 +5,7 @@
 
 # run short-benchmarks for relay chain runtimes from polkadot
 
-short-benchmark-polkadot: &short-bench
+short-benchmark-westend: &short-bench
   stage: short-benchmarks
   extends:
     - .docker-env
@@ -14,22 +14,12 @@ short-benchmark-polkadot: &short-bench
     - job: build-short-benchmark
       artifacts: true
   variables:
-    RUNTIME: polkadot
+    RUNTIME: westend
   tags:
     - benchmark
   script:
     - ./artifacts/polkadot benchmark pallet --chain $RUNTIME-dev --pallet "*" --extrinsic "*" --steps 2 --repeat 1
 
-short-benchmark-kusama:
-  <<: *short-bench
-  variables:
-    RUNTIME: kusama
-
-short-benchmark-westend:
-  <<: *short-bench
-  variables:
-    RUNTIME: westend
-
 # run short-benchmarks for system parachain runtimes from cumulus
 
 .short-benchmark-cumulus: &short-bench-cumulus