Remove use of _usesRoles helper.

lib/authn.js

@@ -35,13 +35,6 @@ export async function openDatabase(options) {
   const serverInfo = await admin.serverInfo(null);
   _checkServerVersion({serverInfo, config});
 
-  // check if server supports roles; if not, can't authenticate
-  if(!_usesRoles(serverInfo)) {
-    const stringVersion = serverInfo.versionArray.join('.');
-    throw new BedrockError(
-      `MongoDB server version "${stringVersion}" is unsupported.`,
-      'NotSupportedError');
-  }
   // makes an unauthenticated call to the server
   // to see if auth is required
   const authRequired = await _isAuthnRequired({config, admin});
@@ -88,13 +81,6 @@ async function _connect(options) {
   return {client, db};
 }
 
-function _usesRoles(serverInfo) {
-  // >= Mongo 2.6 uses user roles
-  return (
-    (serverInfo.versionArray[0] == 2 && serverInfo.versionArray[1] >= 6) ||
-    (serverInfo.versionArray[0] > 2));
-}
-
 /**
  * Determines if authn is required.
  *