net/pimcommon: remove unnecessary dependency on webkit

Was ported to webengine upstream in [1] and later removed in [2].

[1] https://invent.kde.org/pim/pimcommon/-/commit/ef6ec3974af5e535a7d4133131b668939927676a
[2] https://invent.kde.org/pim/pimcommon/-/commit/5fe9c0484fb305a358b70c807f83d6cca30d180a