Drivers: hv: vmbus: Remove vmbus_sendpacket_pagebuffer()

With the netvsc driver changed to use vmbus_sendpacket_mpb_desc()
instead of vmbus_sendpacket_pagebuffer(), the latter has no remaining
callers. Remove it.

Cc: <stable@vger.kernel.org> # 6.1.x
Signed-off-by: Michael Kelley <mhklinux@outlook.com>
Link: https://patch.msgid.link/20250513000604.1396-6-mhklinux@outlook.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>