Revert "Fix glyph selections spanning multiple Unicode grapheme clusters"

This reverts commit d5e81a4d6949049d2bb90d1b7be26908fefb8ae9.

Reason for revert: Likely the culprit of crbug.com/1471444

Original change's description:
> Fix glyph selections spanning multiple Unicode grapheme clusters
>
> Abandon the proportional equal division method,
> calculate the actual Unicode grapheme cluster of current character,
> judge whether the current character and the previous character
> are in the same Unicode grapheme cluster to confirm
> whether the current character is the first character
> of the current Unicode grapheme cluster.
>
> Bug: 1465250
> Change-Id: I1c494028276e7c8f8cd88a280104dd0d51e0f363
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4740422
> Commit-Queue: Koji Ishii <kojii@chromium.org>
> Reviewed-by: Koji Ishii <kojii@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#1181370}

Bug: 1465250, 1471444
Change-Id: I4f87d2517564d98722c932677a3f53033872ca16
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4765370
Commit-Queue: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Auto-Submit: Felipe Andrade <fsandrade@chromium.org>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Owners-Override: Felipe Andrade <fsandrade@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1181438}