all: drop unused variables

Keeps build with GCC 8 happy.

mm-base-call.c:758:18: warning: variable 'response' set but not used [-Wunused-but-set-variable]
mm-base-call.c:822:18: warning: variable 'response' set but not used [-Wunused-but-set-variable]
mm-base-sms.c:908:18: warning: variable 'response' set but not used [-Wunused-but-set-variable]
mm-sms-list.c:331:25: warning: variable 'ctx' set but not used [-Wunused-but-set-variable]
mm-iface-modem-messaging.c:1210:21: warning: variable 'storage_ctx' set but not used [-Wunused-but-set-variable]
huawei/mm-plugin-huawei.c:183:18: warning: variable 'response' set but not used [-Wunused-but-set-variable]
ublox/mm-plugin-ublox.c:161:24: warning: variable 'response' set but not used [-Wunused-but-set-variable]
ublox/mm-plugin-ublox.c:159:24: warning: variable 'ctx' set but not used [-Wunused-but-set-variable]
icera/mm-modem-helpers-icera.c:218:25: warning: variable 'first_free' set but not used [-Wunused-but-set-variable]
novatel/mm-common-novatel.c:50:18: warning: variable 'response' set but not used [-Wunused-but-set-variable]

src/mm-base-call.c

@@ -755,11 +755,10 @@ call_hangup_ready (MMBaseModem *modem,
 {
     MMBaseCall *self;
     GError *error = NULL;
-    const gchar *response;
 
     self = g_task_get_source_object (task);
 
-    response = mm_base_modem_at_command_finish (modem, res, &error);
+    mm_base_modem_at_command_finish (modem, res, &error);
     if (error) {
         if (g_error_matches (error, MM_SERIAL_ERROR, MM_SERIAL_ERROR_RESPONSE_TIMEOUT)) {
             g_task_return_error (task, error);
@@ -819,9 +818,8 @@ call_send_dtmf_ready (MMBaseModem *modem,
                       GTask *task)
 {
     GError *error = NULL;
-    const gchar *response = NULL;
 
-    response = mm_base_modem_at_command_finish (modem, res, &error);
+    mm_base_modem_at_command_finish (modem, res, &error);
     if (error) {
         mm_dbg ("Couldn't send_dtmf: '%s'", error->message);
         g_task_return_error (task, error);

src/mm-base-sms.c

@@ -905,10 +905,9 @@ store_ready (MMBaseModem *modem,
              GTask *task)
 {
     SmsStoreContext *ctx;
-    const gchar *response;
     GError *error = NULL;
 
-    response = mm_base_modem_at_command_finish (modem, res, &error);
+    mm_base_modem_at_command_finish (modem, res, &error);
     if (error) {
         g_task_return_error (task, error);
         g_object_unref (task);

src/mm-iface-modem-messaging.c

@@ -1207,10 +1207,8 @@ init_current_storages_ready (MMIfaceModemMessaging *self,
                              GTask *task)
 {
     InitializationContext *ctx;
-    StorageContext *storage_ctx;
     GError *error = NULL;
 
-    storage_ctx = get_storage_context (self);
     if (!MM_IFACE_MODEM_MESSAGING_GET_INTERFACE (self)->init_current_storages_finish (
             self,
             res,

src/mm-sms-list.c

@@ -328,11 +328,6 @@ mm_sms_list_take_part (MMSmsList *self,
                        MMSmsStorage storage,
                        GError **error)
 {
-    PartIndexAndStorage ctx;
-
-    ctx.part_index = mm_sms_part_get_index (part);
-    ctx.storage = storage;
-
     /* Ensure we don't have already taken a part with the same index */
     if (mm_sms_list_has_part (self,
                               storage,