connector/ldap: use gopkg.in/ldap.v2's escape filter

Use the escape filter method provided by the upstream LDAP package
instead of rolling our own.

connector/ldap/ldap_test.go

@@ -1,23 +0,0 @@
-package ldap
-
-import "testing"
-
-func TestEscapeFilter(t *testing.T) {
-	tests := []struct {
-		val  string
-		want string
-	}{
-		{"Five*Star", "Five\\2aStar"},
-		{"c:\\File", "c:\\5cFile"},
-		{"John (2nd)", "John \\282nd\\29"},
-		{string([]byte{0, 0, 0, 4}), "\\00\\00\\00\\04"},
-		{"Chloé", "Chlo\\c3\\a9"},
-	}
-
-	for _, tc := range tests {
-		got := escapeFilter(tc.val)
-		if tc.want != got {
-			t.Errorf("value %q want=%q, got=%q", tc.val, tc.want, got)
-		}
-	}
-}