Update project pull request template (#7934)

This commit streamlines the project's GitHub pull request template. Primarily, it removes white space between bullet items, which add unnecessary visual bulk to new pull requests. It also rewords a code comment and removes one that seems to reference deprecated systems.

Author: semioticrobotic

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,24 +1,12 @@
 <!-- Thank you for submitting a contribution to Apache Geode. -->
 
-<!-- In order to streamline the review of the contribution we ask you
-to ensure the following steps have been taken: 
--->
+<!-- In order to streamline review of your contribution we ask that you
+ensure you've taken the following steps. -->
 
-### For all changes:
+### For all changes, please confirm:
 - [ ] Is there a JIRA ticket associated with this PR? Is it referenced in the commit message?
-
 - [ ] Has your PR been rebased against the latest commit within the target branch (typically `develop`)?
-
 - [ ] Is your initial contribution a single, squashed commit?
-
 - [ ] Does `gradlew build` run cleanly?
-
 - [ ] Have you written or updated unit tests to verify your changes?
-
 - [ ] If adding new dependencies to the code, are these dependencies licensed in a way that is compatible for inclusion under [ASF 2.0](http://www.apache.org/legal/resolved.html#category-a)?
-
-<!-- Note:
-Please ensure that once the PR is submitted, check Concourse for build issues and
-submit an update to your PR as soon as possible. If you need help, please send an
-email to dev@geode.apache.org.
--->