Deprecate rarely or unused *LinkAttributes methods in Linker

Linker::getInterwikiLinkAttributes and Linker::getInternalLinkAttributesObj
are not not used any code in gerrit.

Linker::getInternalLinkAttributes is used once, in the Video extension.

Change-Id: I76d9b549e0fdccb9c1b4d9c12ba40a67c2733637
Merge "Deprecate rarely or unused *LinkAttributes methods in Linker"