Revert "go/printer: reuse go/token.FileSet.PositionFor calls in setPos"

This reverts commit http://go.dev/cl/461739

Reason for revert: Causes longtest failures due to odd formatting.

Change-Id: I7e31ff107e730b6d667866ea7718bc8632760422
Reviewed-on: https://go-review.googlesource.com/c/go/+/483676
Reviewed-by: Russ Cox <[email protected]>
Run-TryBot: Than McIntosh <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>

Author: thanm

src/go/printer/printer.go

@@ -878,12 +878,8 @@ func mayCombine(prev token.Token, next byte) (b bool) {
 }
 
 func (p *printer) setPos(pos token.Pos) {
-	// If p.pos is already equivalent to pos,
-	// we can avoid calling posFor again.
 	if pos.IsValid() {
-		if file := p.fset.File(pos); file != nil && file.Offset(pos) != p.pos.Offset {
-			p.pos = p.posFor(pos) // accurate position of next item
-		}
+		p.pos = p.posFor(pos) // accurate position of next item
 	}
 }