Enhance Settings deep link transition

Since the deep link mechanism uses a trampoline activity to redirect the
target activity, and the targeting activity is launched in a separate
task, there will be two transitions played, where one is the splash
screen with the trampoline acitvity and another one is the task
transition. This makes the UX weird.

To avoid this, this CL tries to make the targeting activity launch in
the same task as the trampoline acitivity by removing the taskAffinity,
so there won't be a task transition.

Fix: 215275940
Test: Create a settings shortcut on the home screen and launch it.
Change-Id: I7621ab9f1132acbf619495801a3b985c5c3b1b5d