Use one character instead of line drawings.

This is more consistent with the name of the operator,
and avoids graphical artifacts in some tools like Dymola.
(The new variant works with and without anti-aliasing, the old
one worked with neither.)

Complex.mo

@@ -76,8 +76,10 @@ operator record Complex "Complex number with overloaded operators"
             lineColor={128,128,128},
             extent={{-100,-100},{100,100}},
             radius=25.0),
-          Line(
-            points={{-50,0},{50,0}})}));
+          Text(
+            extent={{-100,100},{100,-80}},
+            textColor={128,128,128},
+            textString="-")}));
   end '-';
 
   encapsulated operator '*' "Multiplication"
@@ -131,14 +133,10 @@ operator record Complex "Complex number with overloaded operators"
             lineColor={128,128,128},
             extent={{-100,-100},{100,100}},
             radius=25.0),
-          Line(
-            points={{-42,36},{39,-34}}),
-          Line(
-            points={{-42,-35},{39,37}}),
-          Line(
-            points={{-55,1},{52,1}}),
-          Line(
-            points={{-1.5,55},{-2,-53}})}));
+          Text(
+            extent={{-100,46},{102,-100}},
+            textColor={128,128,128},
+            textString="*")}));
   end '*';
 
   encapsulated operator function '+' "Add two complex numbers"