[dev.typeparams] test: enable excluded test fixedbugs/issue7742.go

The test is fine and probably was excluded by mistake.

Change-Id: I98508e603afe01a781ad7c8638830514aa75939c
Reviewed-on: https://go-review.googlesource.com/c/go/+/286732
Trust: Robert Griesemer <gri@golang.org>
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

test/run.go

@@ -1985,6 +1985,5 @@ var excluded = map[string]bool{
 	"fixedbugs/issue7525c.go":  true, // types2 reports init cycle error on different line - ok otherwise
 	"fixedbugs/issue7525d.go":  true, // types2 reports init cycle error on different line - ok otherwise
 	"fixedbugs/issue7525e.go":  true, // types2 reports init cycle error on different line - ok otherwise
-	"fixedbugs/issue7742.go":   true, // types2 type-checking doesn't terminate
 	"fixedbugs/issue7746.go":   true, // types2 type-checking doesn't terminate
 }