[FEM] fix the Elmer solver writer

- fixes #6604
as it was, Elmer was almost unusable because most values were input with wrong units to Elmer.
Elmer uses pure SI units

ToDo: fix the still wrong Vacuum permittivity

src/Mod/Fem/femtaskpanels/task_constraint_electrostaticpotential.py

@@ -126,7 +126,7 @@ class _TaskPanel(object):
             not self._paramWidget.potentialBox.isChecked()
         if self._obj.PotentialEnabled:
             # if the input widget shows not a green hook, but the user presses ok
-            # we could run into a syntax error on getting the quantity, try mV
+            # we could run into a syntax error on getting the quantity
             quantity = None
             try:
                 quantity = Units.Quantity(self._paramWidget.potentialTxt.text())