regexp/syntax: remove unused flags parameter

Found by github.com/mvdan/unparam.

Change-Id: I186d2afd067e97eb05d65c4599119b347f82867d
Reviewed-on: https://go-review.googlesource.com/37840Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/regexp/syntax/parse.go

@@ -381,7 +381,7 @@ func (p *parser) collapse(subs []*Regexp, op Op) *Regexp {
 		}
 	}
 	if op == OpAlternate {
-		re.Sub = p.factor(re.Sub, re.Flags)
+		re.Sub = p.factor(re.Sub)
 		if len(re.Sub) == 1 {
 			old := re
 			re = re.Sub[0]
@@ -402,7 +402,7 @@ func (p *parser) collapse(subs []*Regexp, op Op) *Regexp {
 // which simplifies by character class introduction to
 //     A(B[CD]|EF)|BC[XY]
 //
-func (p *parser) factor(sub []*Regexp, flags Flags) []*Regexp {
+func (p *parser) factor(sub []*Regexp) []*Regexp {
 	if len(sub) < 2 {
 		return sub
 	}