Simplify updatedAmount calculation in LineItem changeFeeSelections()

[mattwire]

Overview

Partial from #32222

Currently we count the number of participants or the number of memberships and if count > 0 we calculate the updated lineItem amount.
However, if we just calculate the updated amount that's one query instead of at least two and we get to simplify the code.

Before

Checking counts before calculating updated amount.

After

Just calculate updated amount.

Technical Details

Comments

[civibot]

🤖 Thank you for contributing to CiviCRM! ❤️ We will need to test and review this PR. 👷

Introduction for new contributors...

• If this is your first PR, an admin will greenlight automated testing with the command ok to test or add to whitelist.
• A series of tests will automatically run. You can see the results at the bottom of this page (if there are any problems, it will include a link to see what went wrong).
• A demo site will be built where anyone can try out a version of CiviCRM that includes your changes.
• If this process needs to be repeated, an admin will issue the command test this please to rerun tests and build a new demo site.
• Before this PR can be merged, it needs to be reviewed. Please keep in mind that reviewers are volunteers, and their response time can vary from a few hours to a few weeks depending on their availability and their knowledge of this particular part of CiviCRM.
• A great way to speed up this process is to "trade reviews" with someone - find an open PR that you feel able to review, and leave a comment like "I'm reviewing this now, could you please review mine?" (include a link to yours). You don't have to wait for a response to get started (and you don't have to stop at one!) the more you review, the faster this process goes for everyone 😄
• To ensure that you are credited properly in the final release notes, please add yourself to contributor-key.yml
• For more information about contributing, see CONTRIBUTING.md.

Quick links for reviewers...

• ➡️ PR Demo site (can be rebuilt with the command test this please).
• 📖 Review standards
• 🗒️ Review template (brief or verbose)

➡️ Online demo of this PR 🔗