wt-status: lift the artificual "at least 20 columns" floor

wt-status: lift the artificual "at least 20 columns" floor

When we show unmerged paths, we had an artificial 20 columns floor
for the width of labels (e.g. "both deleted:") shown next to the
pathnames.  Depending on the locale, this may result in a label that
is too wide when all the label strings are way shorter than 20
columns, or no-op when a label string is longer than 20 columns.

Just drop the artificial floor.  The screen real estate is better
utilized this way when all the strings are shorter.

Adjust the tests to this change.

Signed-off-by: Junio C Hamano <gitster@pobox.com>