powerpc/configs: Drop NET_VENDOR_HP which moved to staging

The HP network driver moved to staging in commit 52340b82

 ("hp100:
Move 100BaseVG AnyLAN driver to staging") meaning we don't need to
disable it any more in our defconfigs.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Acked-by: Joel Stanley <joel@jms.id.au>
Link: https://lore.kernel.org/r/20200121043000.16212-3-mpe@ellerman.id.au