docs/driver-api/miscellaneous: Remove kernel-doc of serial_core.c

Since merge of tty-6.0-rc1, "make htmldocs" with Sphinx >=3.1 emits
a bunch of warnings indicating duplicate kernel-doc comments from
drivers/tty/serial/serial_core.c.

This is due to the kernel-doc directive for serial_core.c in
serial/drivers.rst added in the merge. It conflicts with an existing
kernel-doc directive in miscellaneous.rst.

Remove the latter directive and resolve the duplicates.

Signed-off-by: Akira Yokosawa <akiyks@gmail.com>
Fixes: 607ca0f742b7 ("Merge tag 'tty-6.0-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty")
Cc: stable@vger.kernel.org # 6.0
Cc: Jiri Slaby <jslaby@suse.cz>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Jiri Slaby <jirislaby@kernel.org>
Link: https://lore.kernel.org/r/4e54c76a-138a-07e0-985a-dd83cb622208@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>