math/wxmaxima: Remove obsolete patch

According to 20200115 entry of CHANGES man pages can (and should) now be
installed in ${PREFIX}/share/man. This obsoletes
wxmaxima/files/patch-data_CMakeLists.txt.

While here I also fixed sorting in pkg-plist.

Approved by: gerald (mentor)
Differential Revision: https://reviews.freebsd.org/D24205