duplicate item in see also.

Ok, I know legmul is important, I'm not sure I need it twice.

Joking aside, I belive that's a wrong copy-past, as other functions have
`legmulx, legmul`, but as this is the docs of legmulx, I guess the
author removed the `x` without realising legmul was already present.

Author: Carreau

numpy/polynomial/legendre.py

@@ -425,7 +425,7 @@ def legmulx(c):
 
     See Also
     --------
-    legadd, legmul, legmul, legdiv, legpow
+    legadd, legmul, legdiv, legpow
 
     Notes
     -----