git-gui: Remove the loaded column from the blame viewer

git-gui: Remove the loaded column from the blame viewer

Originally I had placed this loaded column between the line number
and the file line data to help users know if a particular line has
received annotation data or not yet.  This way users would know if
the line(s) they were interested in were ready for viewing, or if
they still had to wait.  It also was an entertaining way for the
user to spend their time waiting for git-blame --incremental to
compute the complete set of annotations.

However it is completely useless now that we show the abbreviated
commit SHA-1 and author initials in the leftmost column.  That area
is empty until we get the annotation data, and as soon as we get it
in we display something there, indicating to the user that there is
now blame data ready.  Further with the tooltips the user is likely
to see the data as soon as it comes in, as they are probably not
keeping their mouse perfectly still.  So I'm removing the field to
save screen space for more useful things, like file content.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>