exec: kill ->load_binary != NULL check in search_binary_handler()

exec: kill ->load_binary != NULL check in search_binary_handler()

search_binary_handler() checks ->load_binary != NULL for no reason, this
method should be always defined.  Turn this check into WARN_ON() and move
it into __register_binfmt().

Also, kill the function pointer.  The current code looks confusing, as if
->load_binary can go away after read_unlock(&binfmt_lock).  But we rely on
module_get(fmt->module), this fmt can't be changed or unregistered,
otherwise this code is buggy anyway.

Signed-off-by: Oleg Nesterov <[email protected]>
Acked-by: Kees Cook <[email protected]>
Cc: Al Viro <[email protected]>
Cc: Evgeniy Polyakov <[email protected]>
Cc: Zach Levis <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>