docs: remove Gitter from issue templates

[ersachin3112]

This PR contains a:

• [ ] bugfix
• [ ] new feature
• [ ] code refactor
• [ ] test update
• [ ] typo fix
• [x] metadata update

Motivation / Use-Case

remove Gitter from issue templates

Breaking Changes

No

Additional Info

No

[codecov[bot]]

Codecov Report

Patch and project coverage have no change.

Comparison is base (f2cea2f) 90.54% compared to head (505a7ea) 90.54%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #1037 +/- ## ======================================= Coverage 90.54% 90.54% ======================================= Files 5 5 Lines 857 857 Branches 243 243 ======================================= Hits 776 776 Misses 71 71 Partials 10 10 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Do you have feedback about the report comment? Let us know in this issue.