dragging a block out of the flyout should not cause 'save now' to appear

[chrisgarrity]

Expected Behavior

Please describe what should happen
If you drag a block out of the flyout, but don't actually add it to the workspace, the project should not appear to be 'changed'

Actual Behavior

Describe what actually happens
'save now' appears in the nav bar, and an auto-save will happen.

Steps to Reproduce

Explain what someone needs to do in order to see what's described in Actual behavior above
Drag a block out of the flyout, but don't drop it in the workspace. Either drop it back in the flyout to delete it, or in the backpack.

This may be a scratch-blocks bug, but adding it to gui because of the backpack interaction.

[kchadha]

Related to scratchfoundation/scratch-vm#2030 which lists some other cases as well.