Remove an unused local variable (#279)

LGTM flagged this up in another PR, submitting separately keeps the comment noise down.
Flake8 also flagged it.

Author: eric-wieser

galgebra/metric.py

@@ -440,7 +440,7 @@ def _build_derivatives_of_basis(self):  # Derivatives of basis vectors from Chri
 
         n_range = self.n_range
 
-        self.dg = dg = self.derivatives_of_g()
+        self.dg = self.derivatives_of_g()
 
         self._init_connect_flg()
 

setup.cfg

@@ -37,8 +37,7 @@ per-file-ignores =
     ./galgebra/ga.py:E266
 
     # F821 undefined name 'Mv'
-    # F841 local variable 'dg' is assigned to but never used
-    ./galgebra/metric.py:F821,F841
+    ./galgebra/metric.py:F821
 
     # E266 too many leading '#' for block comment
     ./galgebra/mv.py:E266