Consider removing MLBufferView in its current form

[a-sully]

Building on #546 and #553

In the Chromium implementation, the Model Loader API spec, and - soon, once #553 merges - the WebNN spec, MLBufferView is specified as:

typedef ArrayBufferView MLBufferView;

This was intended to be forward-looking (let's be prepared for when we start using hardware accelerators?!) to provide a "view over some device-agnostic buffer", but at this point:

1. We're ready to use hardware accelerators; MLBuffer is our proposed solution for a device-agnostic buffer (see Support for device-based tensor storage objects #482)
2. It's unclear whether a typedef is sufficient to provide the "view over an MLBuffer" that MLBufferView was initially intending to provide, and
3. This typedef is not adding any value otherwise

As @bbernhar pointed out in #553 (comment), we'll still likely want the ability to take a view over an MLBuffer. However, I (personally) think it's more likely this ends up looking more like a GpuBufferBinding than a typedef

Given all this, I propose we remove MLBufferView in its current form for now, and then we can discuss the specifics of how to take a view over an MLBuffer at a later time