Add deprecation warnings for log related methods

* LogEventsList::getDisplayTitle() was deprecated in 1.20.
* LogPage::logHeader() was deprecated in 1.19.
* LogPage::logName() was deprecated in 1.19.

No remaining uses in core.

Change-Id: I073f11a7776f6e3809d20d50e61e57486b77f494
Merge "Add deprecation warnings for log related methods"