(bug 42337) Simplify "my talk" link logic in personal tools

(bug 42337) Simplify "my talk" link logic in personal tools

Change I822a7390 introduced a somewhat complex way to display
the "talk" link in parentheses after the username. It would only
work in Vector, and it broke the display in RTL wikis, because
it hacked into the personal links array.

This change attempts to make it more robust, by keeping the
array intact and adding the parentheses to the mytalk item
as a special case in SkinTemplate::makeListItem(). This fixes
the display in RTL wikis and allows the parentheses
to be displayed in all skins.

This commit also eliminates the global $wgVectorCombineUserTalk,
which is not needed any more.

Change-Id: I36ec3bec89a17cab3e4fc56ccf5038f7df93d213