include: drop nm-settings-flags.h, move NMSecretAgentGetSecretsFlags

For some reason, the flags used by o.fd.NM.SecretAgent.GetSecrets were
defined as both NMSecretAgentGetSecretsFlags in
libnm{,-glib}/nm-secret-agent.h, and then separately as
NMSettingsGetSecretsFlags in include/nm-settings-flags.h.
(NMSettingsGetSecretsFlags also had an additional internal-use-only
value, but that was added later after the duplication already
existed.)

Fix this by moving NMSecretAgentGetSecretsFlags from libnm to
nm-dbus-interface.h, adding the internal-use-only value to it as well,
updating the core code to use that, and then removing
nm-settings-flags.h.

src/nm-activation-request.h

@@ -27,7 +27,6 @@
 #include "nm-types.h"
 #include "nm-connection.h"
 #include "nm-active-connection.h"
-#include "nm-settings-flags.h"
 
 #define NM_TYPE_ACT_REQUEST            (nm_act_request_get_type ())
 #define NM_ACT_REQUEST(obj)            (G_TYPE_CHECK_INSTANCE_CAST ((obj), NM_TYPE_ACT_REQUEST, NMActRequest))
@@ -72,7 +71,7 @@ typedef void (*NMActRequestSecretsFunc) (NMActRequest *req,
 
 guint32 nm_act_request_get_secrets (NMActRequest *req,
                                     const char *setting_name,
-                                    NMSettingsGetSecretsFlags flags,
+                                    NMSecretAgentGetSecretsFlags flags,
                                     const char *hint,
                                     NMActRequestSecretsFunc callback,
                                     gpointer callback_data);