cue/build: remove unnecessary duplicate initialized

Change-Id: Icce5dae2495c1eacd3afeafac09c40696cd9912b
Reviewed-on: https://cue-review.googlesource.com/c/cue/+/4503
Reviewed-by: Marcel van Lohuizen <mpvl@golang.org>
diff --git a/cue/build/context.go b/cue/build/context.go
index 94cc2a5..664326e 100644
--- a/cue/build/context.go
+++ b/cue/build/context.go
@@ -81,7 +81,6 @@
 	if !c.initialized {
 		c.initialized = true
 		c.ctxt = context.Background()
-		c.initialized = true
 		c.imports = map[string]*Instance{}
 	}
 }