[REF] DAO - Consolidate redundant functions keys() and getPrimaryKey()

[colemanw]

Overview

Followup to 615f874
Towards dev/core#4999

Technical Details

The getPrimaryKey() function was added recently and the older one was hobbled by not returning the declared $_primaryKey. Fortunately the new function was protected so could be safely removed while fixing keys() to do the right thing.

Comments

Also removes some useless static caching; it's already a static class variable it doesn't need to be statically cached again.

[civibot]

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[totten]

Yeah, I can't find any references to this in universe.

[totten]

it's already a static class variable it doesn't need to be statically cached again.

Did you consider going the other way? Maybe a third static variable?