Cleanup: Remove unused variable (#6581)

Signed-off-by: Tobias Guggenmos <tguggenm@redhat.com>

promql/parse.go

@@ -31,7 +31,6 @@ import (
 type parser struct {
 	lex   *Lexer
 	token Item
-	peeking bool
 
 	inject    Item
 	injecting bool
@@ -134,16 +133,12 @@ func (p *parser) typecheck(node Node) (err error) {
 
 // next returns the next token.
 func (p *parser) next() Item {
-	if !p.peeking {
 	t := p.lex.NextItem()
 	// Skip comments.
 	for t.Typ == COMMENT {
 		t = p.lex.NextItem()
 	}
 	p.token = t
-	}
-
-	p.peeking = false
 
 	if p.token.Typ == ERROR {
 		p.errorf("%s", p.token.Val)