Update .gitignore to exclude PHPUnit cache files and backup configuration; remove obsolete PHPUnit configuration and cache result files.

Author: farhadzand

.gitignore

@@ -4,3 +4,5 @@
 composer.lock
 /.phpunit.result.cache
 /build/*
+phpunit.xml.bak
+.phpunit.cache

.phpunit.cache/test-results

@@ -104,4 +104,4 @@
     },
     "minimum-stability": "stable",
     "prefer-stable": true
-}
+}