cmd/compile: remove unused func nodfltconst

Its only usage was removed in golang.org/cl/103860

Change-Id: I2a230b9475b0aadf3892b89f5e4ee6d4c5b70394
Reviewed-on: https://go-review.googlesource.com/c/go/+/172917Reviewed-by: Keith Randall <khr@golang.org>
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

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

@@ -416,12 +416,6 @@ func nodintconst(v int64) *Node {
 	return nodlit(Val{u})
 }
 
-func nodfltconst(v *Mpflt) *Node {
-	u := newMpflt()
-	u.Set(v)
-	return nodlit(Val{u})
-}
-
 func nodnil() *Node {
 	return nodlit(Val{new(NilVal)})
 }