media: dib9000: delete some unused broken code

The dib9000_remove_slave_frontend() function isn't used.

I was reviewing it because my static checker claims it writes one
element beyond the end of the array.  That's a false positive.  What it
actually does is, if there are two or more front ends, then it prints a
debug message to say that it removed the first one, stored in
state->fe[1], and then it "removes" (scare quotes on purpose) the second
one, stored in state->fe[2].  Deleting a front end from the middle is
not really supported and breaks code like dib9000_release() which
assumes the first NULL front end marks the end of the list.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>