Simplify math in StripLayoutHelper.calculateDeltaToMakeTabVisible

It's worth noting that we don't need to handle LTR/RTL in the method
since:
* all the calculations are under the window coordinate system, which
  is the same for LTR and RTL layouts, and
* the returned value is also a 1-D vector on the X axis under the
  window coordinate system.

The above is the current logic in essence. This CL simplifies it by:
* removing LTR/RTL checks, and
* simplifying the formulas (e.g., scrollOffset gets cancelled out
  eventually).

This CL doesn't cause any behavior change. The simplification will
help debug issues like the attached bug.

Bug: 369284016
Change-Id: I0ed141d4492ec4dc61842394579420bfdbc335fc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6489712
Reviewed-by: Neil Coronado <nemco@google.com>
Reviewed-by: Zhe Li <zheliooo@google.com>
Commit-Queue: Linyu He <linyuh@google.com>
Cr-Commit-Position: refs/heads/main@{#1451958}