Remove the Plots::GD PG module dependency.

Author: drgrice1

conf/defaults.config

@@ -1279,7 +1279,7 @@ ${pg}{modules} = [
 	[qw(Matrix)],
 	[qw(Multiple)],
 	[qw(PGrandom)],
-	[qw(Plots::Plot Plots::Axes Plots::Data Plots::Tikz Plots::JSXGraph Plots::GD)],
+	[qw(Plots::Plot Plots::Axes Plots::Data Plots::Tikz Plots::JSXGraph)],
 	[qw(Regression)],
 	[qw(Select)],
 	[qw(Units)],