package/jasper: simplify disabling documentation

Replace CMAKE_DISABLE_FIND_PACKAGE_{DOXYGEN,LATEX} by JAS_ENABLE_DOC
which is available (and working as expected) since version 2.0.20 and
https://github.com/jasper-software/jasper/commit/cddb7b199a1c78f3ec0b2c6b8af705588437af4b



Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>