[`RococoGenesisExt`](https://github.com/paritytech/polkadot-sdk/blob/a414ea75/polkadot/node/service/src/chain_spec.rs#L152-L171)
is removed. It was the hack to allow overwriting
`EpochDurationInBlocks`. Removal of `RococGenesisExt` prevents from
manipulating the state to change the runtime constants.

Changes:
- Environment variable which controls the `time::EpochDurationInBlocks`
value was added: `ROCOCO_EPOCH_DURATION` (epoch duration will be set to
the value of env),
- `10,100,600` versions of rococo-runtime are built in CI and put into `polkadot-debug` docker image.

`rococo-runtime` building examples:
- to build runtime for `versi_staging_testnet` which had
EpochDurationInBlocks set to 100:
  ```
ROCOCO_EPOCH_DURATION=100 cargo build --features=fast-runtime -p
rococo-runtime
  ```
- to build runtime for `wococo_development`
  ```
ROCOCO_EPOCH_DURATION=10 cargo build --features=fast-runtime -p
rococ...