Merge pull request #4935 from johanvdw/patch-1

update INSTALL: only GRASS 7 is supported

doc/overview.t2t

@@ -31,10 +31,7 @@ Required build dependencies:
 
 Optional dependencies:
 
-- for GRASS providers and plugin - GRASS >= 6.0.0. QGIS may be compiled with GRASS 6 or GRASS 7.
-  It can also be compiled with both GRASS versions in a single build but only if QGIS
-  is not installed with rpath. The desired GRASS version is chosen on runtime by setting
-  LD_LIBRARY_PATH or PATH.
+- for GRASS providers and plugin - GRASS >= 7.0.0.
 - for georeferencer - GSL >= 1.8
 - for PostGIS support - PostgreSQL >= 8.0.x
 - for gps plugin - gpsbabel