app: Remove 'from' duplication on Run doc

Change-Id: I97855989e32a09d0b0c3309579aa7965d3c72129
Reviewed-on: https://go-review.googlesource.com/1896
Reviewed-by: David Crawshaw <crawshaw@golang.org>

app/app.go

@@ -12,7 +12,7 @@ import (
 
 // Run starts the app.
 //
-// It must be called directly from from the main function and will
+// It must be called directly from the main function and will
 // block until the app exits.
 func Run(cb Callbacks) {
 	run(cb)