media: imon: remove unused function tv2int

Since commit 9c7fd60e951d ("media: rc: Replace timeval with ktime_t in
imon.c"), the function tv2int() is no longer used. Remove it.

Signed-off-by: Sean Young <sean@mess.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>