autotest: fix so that ecw.has_write_support() does not deregister JPEG2000 drivers, which interfere with NITF tests for example

git-svn-id: https://svn.osgeo.org/gdal/trunk@26570 f0d54148-0727-0410-94bb-9a71ac55c965
Merge branch 'trunk' into trunk_mingw