chore: remove unused kreait/firebase-php library (#8672)

Author: jeromegamez

composer.json

@@ -76,7 +76,6 @@
         "opis/closure": "^3.7||^4.0",
         "flix-tech/avro-php": "^5.0.0",
         "phpspec/prophecy-phpunit": "^2.1",
-        "kreait/firebase-php": "^6.9",
         "psr/log": "^2.0||^3.0",
         "dg/bypass-finals": "^1.7",
         "squizlabs/php_codesniffer": "3.*",