tgz: extract using tar-stream directly

we used have a fork of tar-fs. using tar-stream directly gives us
more control

src/storage/interface.js

@@ -56,22 +56,19 @@ async function getAvailableSize(apiConfig) {
     return Number.POSITIVE_INFINITY;
 }
 
-function upload(apiConfig, backupFilePath, sourceStream, callback) {
+async function upload(apiConfig, backupFilePath) {
     assert.strictEqual(typeof apiConfig, 'object');
     assert.strictEqual(typeof backupFilePath, 'string');
-    assert.strictEqual(typeof sourceStream, 'object');
-    assert.strictEqual(typeof callback, 'function');
 
-    // Result: none
-    // sourceStream errors are handled upstream
-
-    callback(new BoxError(BoxError.NOT_IMPLEMENTED, 'upload is not implemented'));
+    // Result: { stream, finish() callback }
+    throw new BoxError(BoxError.NOT_IMPLEMENTED, 'upload is not implemented');
 }
 
 async function exists(apiConfig, backupFilePath) {
     assert.strictEqual(typeof apiConfig, 'object');
     assert.strictEqual(typeof backupFilePath, 'string');
 
+    // Result: boolean if exists or not
     throw new BoxError(BoxError.NOT_IMPLEMENTED, 'exists is not implemented');
 }