Update pull_request_template.md to remove PR link examples

[steveburnett]

Description

Removed manual PR link examples from pull_request_template.md.

Motivation and Context

PR #24354 automatically adds links to the PR to the release note, so manually adding PR links to the release note entry for a PR is now redundant.

I have updated the Release Notes Guidelines to remove the examples of manually adding the PR link.

Impact

New pull requests.

Test Plan

Contributor checklist

• Please make sure your submission complies with our contributing guide, in particular code style and commit standards.
• PR description addresses the issue accurately and concisely. If the change is non-trivial, a GitHub Issue is referenced.
• Documented new properties (with its default value), SQL syntax, functions, or other functionality.
• If release notes are required, they follow the release notes guidelines.
• Adequate tests were added if applicable.
• CI passed.

Release Notes

== NO RELEASE NOTE ==