[processing] remove undefined variable (fix #11118)

Author: alexbruy

python/plugins/processing/algs/grass/GrassUtils.py

@@ -385,6 +385,6 @@ def checkGrassIsInstalled(ignorePreviousState=False):
                     running GRASS algorithms.'
         except:
             return 'Error while checking GRASS installation. GRASS might not \
-                be correctly configured.\n' + s
+                be correctly configured.\n'
 
         GrassUtils.isGrassInstalled = True

python/plugins/processing/algs/grass7/Grass7Utils.py

@@ -387,7 +387,7 @@ def checkGrass7IsInstalled(ignorePreviousState=False):
                     running GRASS GIS 7 algorithms.'
         except:
             return 'Error while checking GRASS GIS 7 installation. GRASS GIS 7 might not \
-                be correctly configured.\n' + s
+                be correctly configured.\n'
 
         Grass7Utils.isGrass7Installed = True