[Shotwell] Remove tag xxx from selected photos

[Dougie Nisbet <dougie highmoor co uk>]

I've a feeling this has come up before but right now it's causing me 
some consternation.

If I select a tag in the left pane, then select multiple images in the 
main thumbnail area, it is possible via right-mouse-click to remove the 
tag from the selected photos. However, this only works when the tag is 
selected in the left pane. If I'm browsing via, e.g, the events, or just 
randomly through the library, and I see a few photos mistagged with the 
same tag, I cannot simply select them then right-click to remove the 
tag. I need to select the tag itself, then locate the selection of 
photos within that selection that are mistagged.