Remove unused key types sr25 and ed25 (#3659)

* Remove unused key types sr25 and ed25.

* Restore in specific files to fix build.

* Fix runtime tests

* Fix keystore test

* Revert typo

* Move keytypes to primitives/src/testing.rs

* More missed items.

* Getting close now.

* Fix example in documentation.

* Update core/application-crypto/src/ed25519.rs

* Update core/application-crypto/src/sr25519.rs

* Bump impl version.