Remove old mongo ext requirement

Author: sokil

composer.json

@@ -19,7 +19,6 @@
     },
     "require": {
         "php": ">=5.3 || ^7.0",
-        "ext-mongo": ">=0.9.0",
         "psr/log": "~1.0",
         "psr/simple-cache": "^1.0",
         "jmikola/geojson": "~1.0",
@@ -32,9 +31,6 @@
         "squizlabs/php_codesniffer": "^2.3",
         "phpmd/phpmd" : "@stable"
     },
-    "provide": {
-        "ext-mongo": "*"
-    },
     "suggest": {
         "sokil/php-mongo-migrator": "Add support of migrations",
         "sokil/php-mongo-bundle": "Symfony Bundle",