PR template: remove backport hints

[joergsteffens]

Backports are now created by pr-tool backport, which uses an own PR template.
Therefore the hints to distinguish between normal PR and backport PR are not required in this template.

Thank you for contributing to the Bareos Project!

Please check

• Short description and the purpose of this PR is present above this paragraph
• Your name is present in the AUTHORS file (optional)

If you have any questions or problems, please give a comment in the PR.

Helpful documentation and best practices

• Git Workflow
• Automatic Sourcecode Formatting
• Check your commit messages
• Boy Scout Rule

Checklist for the reviewer of the PR (will be processed by the Bareos team)

Make sure you check/merge the PR using devtools/pr-tool to have some simple automated checks run and a proper changelog record added.

General

• Is the PR title usable as CHANGELOG entry?
• Purpose of the PR is understood
• Commit descriptions are understandable and well formatted
• Required backport PRs have been created

[arogge]

Thank you!