Remove ActionBar.LayoutParams MarginLayoutParams constructor

Adding this for L caused some fun issues with source compatibility.
Apps that previously passed another MarginLayoutParams subclass to
ActionBar.LayoutParams' constructor started statically linking to a
constructor overload that did not exist on older platform changes with
no other source changes. In the interests of avoiding these headaches
for developers, remove it.

Bug 15933193

Change-Id: I01cf8dfa2341b9d9629331639433b59352e7e15a