17.4.25 insideV (Table Cell Inside Vertical Edges Border)
This element specifies the border which shall be displayed on
all interior vertical edges of the current group of table cells.
[Note: Although individual table cells have no concept
of n internal edge, which would render this property useless
in most cases, it is used to determine the cell borders to
apply to a specific group of cells as part of table
conditional formatting in a table style, for example, the
inside vertical edges on the set of cells in the header row.
end note]

So, I interpret this as insideV/H having meaning only within table
styles, and not when directly applied to a cell. The only
documents I've seen with insideV/H directly applied to a cell seem to
have been created by LO - which dumps them everywhere, redundantly.

Change-Id: Ie76e9af6845cc87b0b847050b031e57d95b1a31b
Reviewed-on: https://gerrit.libreoffice.org/59674
Tested-by: Jenkins
Reviewed-by: Justin Luth <justin_luth@sil.org>
Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>