Facet changes still staged even if you clear the fields before submitting curation

[bduranc]

Issue Type: Bug
Issue Description:

If you curate a facet (type in glob expression) and delete it without clicking "Revert", the change still persists when you submit the curation.

In the following test, I populated the doc and test facets with glob expressions and then quickly removed them by hitting back space until both fields were fully clear. I then proceeded to curate the declared license and release date instead, unaware that my original facet values were still staged behind the scenes. The resulting curation PR was submitted with all changes, including the facets even though that was not my intent.

I then submitted a subsequent curation just for the facets alone, but it did not contain anything (possibly due to conflict from previous one?).

[bduranc]

There have issues in the past with things unintentionally ending up in curation PRs.
clearlydefined/service#677