Revert "Introduce AccessKey type for improved type safety"

[VojtechVitek]

Reverts #46

I'm running into transitive build issues like:

# github.com/0xsequence/quotacontrol/middleware
../../../go/pkg/mod/github.com/0xsequence/quotacontrol@v0.21.0/middleware/middleware_quota.go:77:29: undefined: authcontrol.GetProjectIDFromAccessKey
../../../go/pkg/mod/github.com/0xsequence/quotacontrol@v0.21.0/middleware/middleware_quota.go:84:41: cannot use accessKey (variable of string type authcontrol.AccessKey) as string value in argument to client.FetchKeyQuota
# github.com/0xsequence/builder/api/proto
proto/project.go:72:16: undefined: GenerateAccessKey

I think these breaking changes will need to be coordinated with quotacontrol etc.

@klaidliadon FYI, I'll revert & defer for later, as this is blocking me right now. Do you mind revisiting and reverting the revert PR once you have time to work on this and spread the update everywhere?