ansible-test - Enable unused-import pylint rule (#79912)

This was previously enabled for core. This change enables it for collections.

changelogs/fragments/ansible-test-unused-import-collections.yml

@@ -0,0 +1,2 @@
+minor_changes:
+  - ansible-test - Enable the ``unused-import`` rule for the ``pylint`` sanity test for collections.

test/lib/ansible_test/_util/controller/sanity/pylint/config/collection.cfg

@@ -109,7 +109,6 @@ disable=
     unsupported-delete-operation,
     unsupported-membership-test,
     unused-argument,
-    unused-import,
     unused-variable,
     unspecified-encoding,  # always run with UTF-8 encoding enforced
     use-dict-literal,  # ignoring as a common style issue