cmd/compile: remove all remaining nodeSeq code

Passes toolstash -cmp.

Update #14473.

Change-Id: I2ac5c595d7af7a8da1a7e3945e6a753299446250
Reviewed-on: https://go-review.googlesource.com/20497
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
diff --git a/src/cmd/compile/internal/gc/go.go b/src/cmd/compile/internal/gc/go.go
index 6dc31c3..29b4b54 100644
--- a/src/cmd/compile/internal/gc/go.go
+++ b/src/cmd/compile/internal/gc/go.go
@@ -346,7 +346,7 @@
 
 var maxfltval [NTYPE]*Mpflt
 
-var xtop *NodeList
+var xtop []*Node
 
 var externdcl []*Node
 
@@ -364,7 +364,7 @@
 
 var iota_ int32
 
-var lastconst *NodeList
+var lastconst []*Node
 
 var lasttype *Node