Remove Gitter Chat Link and Badge from Readme

[MohitGupta121]

Explanation

Remove Gitter Chat Link and Badge from Readme

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

[MohitGupta121]

@seanlip PTAL, as we discuss in onboarding-space. Gitter-Chat link broken.

[seanlip]

Thanks @MohitGupta121! One comment.

[seanlip]

Thanks! LGTM.

[BenHenning]

Thanks @MohitGupta121.