modpost: drop unused command line switches

Drop modpost command line switches that are no longer used by
makefile.modpost, upon request from Sam Ravnborg <sam@ravnborg.org>,
who wrote:

    modpost is not supposed to be used outside the kernel build. [...]
    I checked if there were any options supported by modpost that
    was not configurable in Makefile.modpost.
    And I could see that the -M and -K options in getopt() were leftovers.
    The code that used these option was dropped in:
    commit a8773769 ("Kbuild: clear marker out of modpost")

    Could you add a patch that delete these on top of what you already have.

https://lore.kernel.org/lkml/20181020140835.GA3351@ravnborg.org/



Suggested-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Paul Walmsley <paul.walmsley@sifive.com>
Signed-off-by: Paul Walmsley <paul@pwsan.com>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>