gnu: imgui@1.86: Adjust make-flags....* gnu/packages/toolkits.scm (imgui-1.86)[arguments]: Remove the
"-DIMGUI_ENABLE_FREETYPE" make-flag which breaks the display of mangohud, the
only dependent. The "-DImDrawIdx=unsigned int" make-flag was previously
removed, so we can do both by filtering make-flags starting with "-D".
[inputs]: Remove freetype.