…re run.

Remove the redundant tracked loads for the underlying image request; the
load blockers present in the ImageRequest structure perform the same
duty with better accuracy.

This better reflects the text of the specification - rather than
queuing a task to dispatch the load evnet as soon as the document
loader is unblocked, we want to "spin the event loop until there
is nothing that delays the load event in the Document." Spinning
the event loop is a concept that requires running tasks
completely, hence we check the condition before returning to the
start of the event loop.

…lable.