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 (6b76970) 97.83% compared to head (5d13d63) 97.83%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #218 +/- ## ======================================= Coverage 97.83% 97.83% ======================================= Files 5 5 Lines 323 323 Branches 99 99 ======================================= Hits 316 316 Misses 6 6 Partials 1 1 ```

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