.gitattributes: minor clean up

* Alignment for readability.
* Remove files which don't exist in this repo from the list.

.gitattributes

@@ -5,18 +5,14 @@
 # https://www.reddit.com/r/PHP/comments/2jzp6k/i_dont_need_your_tests_in_my_production
 # https://blog.madewithlove.be/post/gitattributes/
 #
-/.gitattributes export-ignore
-/.gitignore export-ignore
-/.phpcs.xml export-ignore
-/.phpcs.xml.dist export-ignore
-/phpcs.xml export-ignore
-/phpcs.xml.dist export-ignore
-/phpunit.xml export-ignore
-/phpunit.xml.dist export-ignore
-/.cache export-ignore
-/.github export-ignore
-/images export-ignore
-/tests export-ignore
+/.cache          export-ignore
+/.github         export-ignore
+/images          export-ignore
+/tests           export-ignore
+.gitattributes   export-ignore
+.gitignore       export-ignore
+.phpcs.xml.dist  export-ignore
+phpunit.xml.dist export-ignore
 
 #
 # Auto detect text files and perform LF normalization