Blender Git Loki

Tracking: Fix "Lock to Selection" option from header causing jump

This change makes the behavior consistent between shortcut and
option from space clip's header.

The only caveat is that the "Lock to Selection" is removed from the
Display popover. This is because it is rather hard to make operator
to render same as regular checkbox. However, shouldn't be a problem
because the setting in popover was redundant.

Differential Revision: https://developer.blender.org/D10423