libedit: Revert r247683 to fix buildworld.

I think r247683 is wrong because libedit.so actually uses symbols from
libcurses.so. Since it breaks the build, revert it now.
Remove a couple of unused include.
callwheelmask and callwheelsize are always greater than zero.
Switch their type to u_int.
MAINTAINERS: Document my maintainership of sh(1).