V4L/DVB (6219): V4L: Int if: Remove [gs]_ext_clk

Remove support for g_ext_clk and s_ext_clk. The same functionality is
now handled by g_ifparm.

Signed-off-by: Sakari Ailus <sakari.ailus@nokia.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>