app-text/gspell: fix enchant dep

app-text/gspell: fix enchant dep

gspell-1.6 only works with enchant-1, thus lock it to its
SLOT and subslot - that way it'll be correct dep whichever
way enchant goes before enchant-2 unmasking (subslots or
parallel-installable slots).

gspell-1.8 only works with 2.1.3+, as expressed in deps.
That's the version which became parallel-installable by
having enchant-2.pc file. No further ABI breaks are anticipated,
thus drop the unauthorized subslot operator dep addition, as
it's >=2.1.3 already and no rebuild concerns on enchant
upgrade, even if enchant remains with subslots.

Package-Manager: Portage-2.3.62, Repoman-2.3.12
Signed-off-by: Mart Raudsepp <leio@gentoo.org>