Fix rebase issues

Author: andrewheard

FirebaseVertexAI/Sources/GenerativeAIService.swift

@@ -199,7 +199,6 @@ struct GenerativeAIService {
 //    }
 
     let encoder = JSONEncoder()
-    encoder.userInfo[CodingUserInfoKey(rawValue: "BackendAPI")!] = firebaseInfo.backendAPI
     urlRequest.httpBody = try encoder.encode(request)
     urlRequest.timeoutInterval = request.options.timeout
 

FirebaseVertexAI/Sources/Types/Internal/BackendAPI.swift

@@ -63,8 +63,7 @@ final class ChatTests: XCTestCase {
         projectID: "my-project-id",
         apiKey: "API_KEY",
         googleAppID: "My app ID",
-        firebaseApp: app,
-        backendAPI: .vertexAI
+        firebaseApp: app
       ),
       apiConfig: APIConfig(service: .vertexAI, version: .v1beta),
       tools: nil,

FirebaseVertexAI/Tests/Unit/ChatTests.swift

@@ -1479,8 +1479,7 @@ final class GenerativeModelTests: XCTestCase {
       projectID: "my-project-id",
       apiKey: "API_KEY",
       googleAppID: "My app ID",
-      firebaseApp: app,
-      backendAPI: .vertexAI
+      firebaseApp: app
     )
   }