Fix part of #3775: RTL Exempted file fixes

[viktoriias]

Explanation

Fixes part of #3775: RTL Exempted file fixes.

• Change app:barrierDirection="right" to app:barrierDirection="end" in topic_practice_subtopic.xml files.
• Remove fixed/non-existing files from the exempt list.

Essential Checklist

• The PR title and explanation each start with "Fix #bugnum: " (If this PR fixes part of an issue, prefix the title with "Fix part of #bugnum: ...".)
• Any changes to scripts/assets files have their rationale included in the PR explanation.
• The PR follows the style guide.
• The PR does not contain any unnecessary code changes from Android Studio (reference).
• The PR is made from a branch that's not called "develop" and is up-to-date with "develop".
• The PR is assigned to the appropriate reviewers (reference).

For UI-specific PRs only

If your PR includes UI-related changes, then:

• Add screenshots for portrait/landscape for both a tablet & phone of the before & after UI changes
• For the screenshots above, include both English and pseudo-localized (RTL) screenshots (see RTL guide)
• Add a video showing the full UX flow with a screen reader enabled (see accessibility guide)
• Add a screenshot demonstrating that you ran affected Espresso tests locally & that they're passing

[viktoriias]

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[viktoriias]

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[viktoriias]

@rt4914 @veena14cs Please review.

[rt4914]

LGTM.

Before vs After Screenshot for reference

[BenHenning]

Thanks @viktoriias! This looks great--glad to see the cleanup!