Remove the CLA confirmation from template

We now use the new CLA tooling which automates this

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,6 +1,3 @@
 <!--
 Thanks for contributing to Spring Security. Please provide a brief description of your pull-request and reference any related issue numbers (prefix references with #).
 -->
-
-<!-- Please also confirm that you have signed the CLA by put an [X] in the box below: -->
-- [] I have signed the CLA