Cleanup: Remove obsolete pre-push git hook

This commit removes the pre-push git hook and its associated install
script.

The pre-push hook was originally implemented to validate changes to
Concourse CI pipeline files before they were pushed to the repository.
Since the project has fully migrated away from Concourse CI and all
related pipeline files have been deleted from the codebase, this hook is
now obsolete and serves no purpose.

Author: tuhaihe

pom.xml

@@ -708,7 +708,6 @@ code or new licensing patterns.
             <exclude>src/tools/make_mkid</exclude>
             <exclude>src/tools/tidy</exclude>
             <exclude>src/tools/find_typedef</exclude>
-            <exclude>src/tools/hooks/pre-push</exclude>
             <exclude>src/tools/valgrind.supp</exclude>
             <exclude>src/tools/pgindent/perltidyrc</exclude>
             <exclude>src/tools/pgindent/README.gpdb</exclude>