MLIBZ-2503: User.me() does not delete newly-empty fields on the SDK

[thomasconner]

Steps to reproduce

1. Log into any web app using kinvey-html5-sdk
2. Check the value of a field in the current user's record to make sure it is non-empty – both in the Console -> Identity -> Users page, and in the client app.
3. In the Console -> Identity -> Users page, manually update/erase the value of the field.
4. In the client app, call user.me() on the current user - the saved active user in the SDK is not updated with the deleted property - the code here merges the updated fields but does not remove deleted properties.

Expected result

The field value should be empty/deleted from the current user's data in the client.

Actual result

The field value still exists that was empty/deleted.

Changes

• Remove merging of data returned in the response from the /_me endpoint. The active user data is now replaced with the data returned in the response from /_me endpoint.

Tests

• Remove irrelevant unit tests due to this change.
• Update an existing unit tests that checks that values are removed correctly.

[heyzooi]

simple and clean! LGTM!