Remove a no longer true reference to the need of setting GDAL_DATA en…

…v variable.

doc/rst/source/explain_-Jproj_full.rst_

@@ -10,8 +10,7 @@
  **-J**\ "*+proj=merc +ellps=WGS84 +units=m*\ " or just glue all parameters like in
  **-J**\ *+proj=merc+ellps=WGS84+units=m*.
 
- Using `EPSG codes <https://spatialreference.org>`_ is also possible (but need the setting of the **GDAL_DATA**
- environment variable to point to the GDAL's *data* sub-directory). For example **-JEPSG:4326** sets
+ Using `EPSG codes <https://spatialreference.org>`_ is also possible. For example **-JEPSG:4326** sets
  the WGS-84 system.
 
  For :doc:`mapproject </mapproject>` and :doc:`grdproject </grdproject>` we can go directly from the