cmd/compile: remove toolstash bandage

Change-Id: Ic33dfccf06681470bec19f66653fda67d9901095
Reviewed-on: https://go-review.googlesource.com/c/go/+/196118
Reviewed-by: Keith Randall <[email protected]>

Author: mdempsky

src/cmd/compile/internal/gc/op_string.go

@@ -704,7 +704,6 @@ const (
 	// statements
 	OBLOCK    // { List } (block of code)
 	OBREAK    // break [Sym]
-	_         // For toolstash -cmp. TODO(mdempsky): Remove.
 	OCASE     // case List: Nbody (List==nil means default)
 	OCONTINUE // continue [Sym]
 	ODEFER    // defer Left (Left must be call)