Fix beforeLoad not being called in some requests

[leonardo-fernandes]

Fix beforeLoad not being called in some requests - initially reported in apache#686

The waitForBeforeload flag was preventing beforeLoad from being called on every GET request.

Platforms affected

• Android
• iOS

Motivation and Context

When using the beforeLoad event, we have noticed that it wasn't triggered in every navigation. The reason was related to the waitForBeforeload flag, which was intermittently set to true and bypassing the beforeLoad event.
This flag doesn't seem to be required, and there's no documentation of why it has been introduced. Some analysis of it has already been done in apache#755

Fixes apache#686

Description

Removed the waitForBeforeload flag from the code.

Testing

Tested with MABS 7.2.

Checklist

• I've run the tests to see all new and existing tests pass
• I added automated test coverage as appropriate for this change
• Commit is prefixed with (platform) if this change only applies to one platform (e.g. (android))
• If this Pull Request resolves an issue, I linked to the issue in the text above (and used the correct keyword to close issues using keywords)
• I've updated the documentation if necessary