Simplify OverviewActionsView layout to avoid unexpected misalignemnt

- Removed the weight=3 space on left/right and replace with gracvity=central_horizontal
- Removed unused oav_three_button_space
- Removed irrelevant layout_gravity (gravity within parent), as the LinearLayout is already taking full parent width, and its vertical alignemnt si controlled by `updateVerticalMargin` in code

Bug: 329255757
Test: OverviewImageTest
Flag: None
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:2cf1a0c08d41ee7a29ea920c93850d3914ed7cd8)
Merged-In: Ice087dde7d3c36b4536d36ce82c382c31c124855
Change-Id: Ice087dde7d3c36b4536d36ce82c382c31c124855