mi: Fix regression in arc drawing

xts' XDrawArcs/15 regressed (turning into a server-side infinite loop)
after:

    commit 7679afd4da8b86aed27e5916ba723116a3c8bb4a
    Author: Adam Jackson <ajax@redhat.com>
    Date:   Fri Sep 26 12:01:37 2014 -0400

        mi: Fold mifpolycon.c into miarc.c

The reason is miarc.c provided its own definitions (sigh) of min/max,
that both accept int arguments and return an int.  Since miFillSppPoly
uses a double (sigh) and some min-involving math for its loop index
variable, things do not go well.

Since the integer versions of min/max are redundant, nuke 'em.

Signed-off-by: Adam Jackson <ajax@redhat.com>
Reviewed-by: Aaron Plattner <aplattner@nvidia.com>
Tested-by: Keith Packard <keithp@keithp.com>
Signed-off-by: Keith Packard <keithp@keithp.com>