Revert "Add $robotPolicy parameter to SpecialPage::setHeaders()"

This reverts commit 8c7541da3b12d4727743ed1d3447f6ac6c3b6846.

Bug: 57883
Change-Id: I582088528286ff34da164fa4457dd203f11df7ef
Merge "Revert "Add $robotPolicy parameter to SpecialPage::setHeaders()""