Remove "final" for VK_SDK_REQUEST_CODE
Remove "final" for VK_SDK_REQUEST_CODE

VK_SDK_REQUEST_CODE must be editable so one can properly register OnActivityResultHandler, which uses a generated request code.
This is required for integration with Corona SDK Enterprise framework, in which you can't override onActivityResult()

Example of usage:
```java
int requestCode = activity.registerActivityResultHandler(new ResultHandler());
VKSdk.VK_SDK_REQUEST_CODE = requestCode;
VKSdk.authorize(permissions, revokeAccess, forceOAuth);
```
vknet/vk-android-sdk,rcsir/vk-android-sdk,Vittt2008/vk-android-sdk,VKCOM/vk-android-sdk,jintoga/vk-android-sdk,VKCOM/vk-android-sdk,Heeby/vk-android-sdk,bossvn/vk-android-sdk