[grass] Drop custom defaultVectorFileExtension implementation

This fixes the GRASS provider ignoring the "default output
vector layer extension" setting for processing. The override
in the grass provider is NOT required as the base class method
already applies the logic for falling back to shp when gpkg
is not available (which was added here in 2e92dab), and
also correctly respects the default format setting.

Fixes #43988

python/plugins/grassprovider/grass_provider.py

@@ -153,15 +153,6 @@ def svgIconPath(self):
     def versionInfo(self):
         return GrassUtils.installedVersion() or None
 
-    def defaultVectorFileExtension(self, hasGeometry=True):
-        # By default,'gpkg', but if OGR has not been compiled with sqlite3, then
-        # we take "SHP"
-        if 'GPKG' in [o.driverName for o in
-                      QgsVectorFileWriter.ogrDriverList()]:
-            return 'gpkg'
-        else:
-            return 'shp' if hasGeometry else 'dbf'
-
     def supportsNonFileBasedOutput(self):
         """
         GRASS Provider doesn't support non file based outputs