distribution: remove vars that shadowed imports or types

distribution: newRepository: don't require RepositoryInfo

This constructor only uses the name / reference, and doesn't
use any of the other properties provided in RepositoryInfo.

distribution: layerDescriptor: don't require RepositoryInfo

This type only uses the name / reference, and doesn't use any of the
other properties provided in RepositoryInfo.

distribution: newPuller: don't require RepositoryInfo

This constructor only uses the name / reference, and doesn't
use any of the other properties provided in RepositoryInfo

distribution: pullEndpoints: don't require RepositoryInfo

The callback only used the name / reference

distribution: pullEndpoints: don't return RepositoryInfo

we're only consuming the name returned.

distribution: pullEndpoints: skip using Service.ResolveRepository

Service.ResolveRepository is a shallow wrapper around newRepositoryInfo,
from which we only consume the Name field. That field is a direct result
of reference.TrimNamed, so we can replace this with that.

distribution; newPusher: don't require RepositoryInfo

This constructor only uses the name / reference, and doesn't
use any of the other properties provided in RepositoryInfo.

distribution: Push: skip using Service.ResolveRepository

Service.ResolveRepository is a shallow wrapper around newRepositoryInfo,
from which we only consume the Name field. That field is a direct result
of reference.TrimNamed, so we can replace this with that.

distribution: GetRepositories skip using Service.ResolveRepository

Service.ResolveRepository is a shallow wrapper around newRepositoryInfo,
from which we only consume the Name field. That field is a direct result
of reference.TrimNamed, so we can replace this with that.

daemon/containerd: registryResolver: remove IsInsecureRegistry

It's not called anywhere, so we can remove it from this interface.

lookup auth-config without depending on RepositoryInfo

Simplify how we lookup auth-config, as we don't need the
additional information provided by RepositoryInfo. There's
still more layers to peel off, which will be done in follow-ups.

registry: ResolveAuthConfig: inline newIndexInfo code

inline a simplified version of "newIndexInfo" without handling of
insecure registries and mirrors, as we don't need that information
to resolve the auth-config.

daemon/containerd: remove registryResolver interface

While it's generally better to define interfaces locally, this one
now duplicated distribution.RegistryResolver, and it's passed on
to other types which expect that interface.

Remove this (un-exported) interface to make it easier to discover
what's used where.

distribution: pushDescriptor: rename repoInfo to repoName

- Human readable description for the release notes

- A picture of a cute animal (not mandatory but encouraged)