Fix data URI scramble (#16098)

* Removed unused method.

* No prefix for data uris.

* Added test to prevent regressions.

modules/markup/html_test.go

@@ -444,3 +444,23 @@ func Test_ParseClusterFuzz(t *testing.T) {
 	assert.NoError(t, err)
 	assert.NotContains(t, res.String(), "<html")
 }
+
+func TestIssue16020(t *testing.T) {
+	setting.AppURL = AppURL
+	setting.AppSubURL = AppSubURL
+
+	var localMetas = map[string]string{
+		"user": "go-gitea",
+		"repo": "gitea",
+	}
+
+	data := `<img src="data:image/png;base64,i//V"/>`
+
+	var res strings.Builder
+	err := PostProcess(&RenderContext{
+		URLPrefix: "https://example.com",
+		Metas:     localMetas,
+	}, strings.NewReader(data), &res)
+	assert.NoError(t, err)
+	assert.Equal(t, data, res.String())
+}