Cleanup x/ccv/types

[shaspitz]

Problem

#1071 has helped illuminate opportunities for cleanup of x/ccv/types. They will be outlined below.

Closing criteria

• Remove unreferenced vars and funcs in x/ccv/codec.go.
• in x/ccv/errors.go, move errors specific to only consumer/provider to their appropriate errors.go file.
• Ditto for events.go
• Split out expected_keepers.go to live in the provider/consumer modules separately, this is best practice for sdk modules.
• Vaguely named consumer structs #1206

Problem details

[MSalopek]

Split out expected_keepers.go to live in the provider/consumer modules separately, this is best practice for sdk modules.

This should be it's own separate issue. Changing it now will break upstream work on upgrading versions etc.