cmd/compile: cull unused ssa construction Error function

The preceding passes have caught any errors
that could occur during SSA construction.

Updates #19250

Change-Id: I736edb2017da3f111fb9f74be12d437b5a24d2b4
Reviewed-on: https://go-review.googlesource.com/38971
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

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

@@ -373,10 +373,6 @@ func (s *state) peekPos() src.XPos {
 	return s.line[len(s.line)-1]
 }
 
-func (s *state) Error(msg string, args ...interface{}) {
-	yyerrorl(s.peekPos(), msg, args...)
-}
-
 // newValue0 adds a new value with no arguments to the current block.
 func (s *state) newValue0(op ssa.Op, t ssa.Type) *ssa.Value {
 	return s.curBlock.NewValue0(s.peekPos(), op, t)