Instantiate lexer inline for the test

Don't use the lex constructor, remove the constructor introduced in the
prevous commit.

promql/lex.go

@@ -428,16 +428,9 @@ func (l *lexer) nextItem() item {
 
 // lex creates a new scanner for the input string.
 func lex(input string) *lexer {
-	return lexWithSeriesDesc(input, false)
-}
-
-// lexWithSeriesDesc creates a  new scanner for the input string
-// and specify seriesDesc to prevent data race in tests
-func lexWithSeriesDesc(input string, seriesDesc bool) *lexer {
 	l := &lexer{
 		input: input,
 		items: make(chan item),
-		seriesDesc: seriesDesc,
 	}
 	go l.run()
 	return l

promql/lex_test.go

@@ -438,7 +438,13 @@ var tests = []struct {
 // for the parser to avoid duplicated effort.
 func TestLexer(t *testing.T) {
 	for i, test := range tests {
-		l := lexWithSeriesDesc(test.input, test.seriesDesc)
+		l := &lexer{
+			input:      test.input,
+			items:      make(chan item),
+			seriesDesc: test.seriesDesc,
+		}
+		go l.run()
+
 		out := []item{}
 		for it := range l.items {
 			out = append(out, it)