Remove dead properties

Remove dead properties

*LogPage::timestamp was introduced with r4919 back in 2004, and is unused
since then.
*ApiMain::mCommit was introduced in r33133, then removed in r33381 but that
line was forgotten.
*SpecialRecentChangesLinked::mResultEmpty was introduced in r36682, then
removed at some point with this leftover.
*SpecialStatistics::hook, introduced in r54511 and unused since then.
*MergeMessageFileList::hasError introduced in Id4b16083435ef7f4fce31861c72889e664d07236
and removed in I3d9cf1d614dacaa91fb2092019ccf1d14d61ccab with a leftover

Change-Id: Ie15c148a3217ee8da62874840f3ef7739893f69e