chore: clean up PR description template (googleapis#1388)

## Description

Removed redundant partitions.

## PR Checklist

> Thank you for opening a Pull Request! Before submitting your PR, there
are a
> few things you can do to make sure it goes smoothly:

- [x] Make sure you reviewed

[CONTRIBUTING.md](https://github.com/googleapis/genai-toolbox/blob/main/CONTRIBUTING.md)
- [ ] Make sure to open an issue as a

[bug/issue](https://github.com/googleapis/genai-toolbox/issues/new/choose)
before writing your code! That way we can discuss the change, evaluate
  designs, and agree on the general idea
- [ ] Ensure the tests and linter pass
- [ ] Code coverage does not decrease (if any source code was changed)
- [ ] Appropriate docs were updated (if necessary)
- [ ] Make sure to add `!` if this involve a breaking change

🛠️ Fixes #<issue_number_goes_here>

---------

Co-authored-by: Wenxin Du <117315983+duwenxin99@users.noreply.github.com>

Author: twishabansal

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,20 +1,18 @@
 ## Description
 
----
 > Should include a concise description of the changes (bug or feature), it's
 > impact, along with a summary of the solution
 
 ## PR Checklist
 
----
 > Thank you for opening a Pull Request! Before submitting your PR, there are a
 > few things you can do to make sure it goes smoothly:
 
 - [ ] Make sure you reviewed
   [CONTRIBUTING.md](https://github.com/googleapis/genai-toolbox/blob/main/CONTRIBUTING.md)
 - [ ] Make sure to open an issue as a
   [bug/issue](https://github.com/googleapis/genai-toolbox/issues/new/choose)
-  before writing your code!  That way we can discuss the change, evaluate
+  before writing your code! That way we can discuss the change, evaluate
   designs, and agree on the general idea
 - [ ] Ensure the tests and linter pass
 - [ ] Code coverage does not decrease (if any source code was changed)