Log Message:
net/ccrtp: Install GNU info files into ${PKGINFODIR}.

This project uses CMake to configure the software.  Force the GNU
info files to be installed into ${CMAKE_INSTALL_INFODIR}, which is
defined by the GNUInstallDirs CMake module included by the
top-level CMakeLists.txt file.  The corrct environment variables
are passed so that ${CMAKE_INSTALL_INFODIR} points into
${PKGINFODIR}.

Remove the subst.mk section that tried to force GNU info files to
be always installed under "info".