remove additional AM_CONDITIONAL definitions
remove additional AM_CONDITIONAL definitions

Remove additional AM_CONDITIONAL definitions for HAVE_LIBCURL
and HAVE_LIBXML2.

Those two AM_CONDITIONALS are already defined by GP_CHECK_LIBRARY.

If not having the addtional definitions exposes a bug, then that
bug should be fixed, not papered over with the additional definitions.

gphoto/libgphoto2,gphoto/libgphoto2,gphoto/libgphoto2,gphoto/libgphoto2,gphoto/libgphoto2,gphoto/libgphoto2