compat_ioctl: remove IGNORE_IOCTL()

Since commit 07d106d0 ("vfs: fix up ENOIOCTLCMD error handling"),
we don't warn about unhandled compat-ioctl command code any more, but
just return the same error that a native file descriptor returns when
there is no handler.

This means the IGNORE_IOCTL() annotations are completely useless and
can all be removed. TIOCSTART/TIOCSTOP and KDGHWCLK/KDSHWCLK fall into
the same category, but for some reason were listed as COMPATIBLE_IOCTL().

Signed-off-by: Arnd Bergmann <arnd@arndb.de>