Remove composer.phar from repository

The 3MB composer.phar binary should not be tracked in git.
It was already listed in .gitignore but had been committed previously.
The sfbuild Makefile target now uses `symfony composer` directly,
consistent with how the build target uses `composer`.

https://claude.ai/code/session_01Y23jrgXnJ6Av6Gf6LdwhMx

Author: claude

Makefile

@@ -45,7 +45,7 @@ build: ## it launches all the build
 	bin/phpunit
 
 sfbuild: ## it launches all the build
-	symfony php composer.phar install
+	symfony composer install
 	PHP_CS_FIXER_IGNORE_ENV=1 symfony php bin/php-cs-fixer fix -v
 	symfony php bin/psalm
 	symfony php bin/phpunit