Improve KeyChain documentation

Improve the choosePrivateKeyAlias documentation by:
(1) removing reference to host+port when a URI is being passed in.
(2) Clearing up the language about what a DPC can do.

Test: N/A
Bug: 81522642
Change-Id: I12fbf675536ea5d843dd2eec4f0379daad764bb6
1 file changed