LP#1441714 Remove 'NO COPIES' in Staff Client

LP#1441714 Remove 'NO COPIES' in Staff Client

When a record has only OPAC invisible items attached to it, the TPAC
displays a 'NO COPIES' message in the staff client.

This fix skips the check for opac visible items when the staff client is
being used.  This can result in incomplete information being displayed in
the summary of the available items because opac invisible items are
often incomplete and do not have shelving locations or libraries
assigned to them.

This fix checks for ctx.is_staff in a number of lines. This results in
holdings being excluded only if the copy is not visible and the
ctx.is_staff variable is not set.

Signed-off-by: Liam Whalen <liam.whalen@bc.libraries.coop>