Remove partial objects from Lisk

Summary:
Ref T4420. This was a performance hack introduced long ago to make typeaheads for users a little cheaper. The idea was that you could load some of an object's columns and skip other ones.

We now always load users on demand, so the cost of loading the whole objects is very small. No other use cases ever arose for this, and it seems unlikely that they will in the future. Remove it all.

Test Plan:
- Grepped for `CONFIG_PARTIAL_OBJECTS`.
- Grepped for `dirtyFields`.
- Grepped for `missingFields`.
- Grepped for `resetDirtyFields`.
- Grepped for `loadColumns`.
- Grepped for `loadColumnsWhere`.
- Grepped for `loadRawDataWhere`.
- Loaded and saved some lisk objects.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T4420

Differential Revision: https://secure.phabricator.com/D9895