cmd/coordinator: remove obsolete reference in comment

subTryBuilders no longer exists, it was factored out into another
package in CL 145157. That logic now happens within the call to
dashboard.TryBuildersForProject function. Remove the reference to it
since it's inaccurate and confusing.

Change-Id: I74d57717541a4ee4fe57f3ae9f46d3fc097cfce1
Reviewed-on: https://go-review.googlesource.com/c/155462
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
diff --git a/cmd/coordinator/coordinator.go b/cmd/coordinator/coordinator.go
index 087d6e7..26eacdd 100644
--- a/cmd/coordinator/coordinator.go
+++ b/cmd/coordinator/coordinator.go
@@ -1092,9 +1092,8 @@
 	// is the Go revision to use to build & test the x/* repo
 	// with. The first element is the master branch. We test the
 	// master branch against all the normal builders configured to
-	// do subrepos (subTryBuilders above). Any GoCommit values past
-	// the first are for older release branches, but we use a limited
-	// subset of builders for those.
+	// do subrepos. Any GoCommit values past the first are for older
+	// release branches, but we use a limited subset of builders for those.
 	var goRev string
 	if len(work.GoCommit) > 0 {
 		goRev = work.GoCommit[0]