bluetooth: CTS: Fix includes to avoid build error with some libCs

Remove unnecessary include in header and source file.

gmtime_r() is an extension to the C library, and therefore one
needs to explicitly ask for its prototype to have it exposed.
This is done by defining _POSIX_C_SOURCE so let's do so.

These two changes fix build errors with some libCs.
Tested with pico, newlib, minimal and the host glibc.

Signed-off-by: Alberto Escolar Piedras <[email protected]>
(cherry picked from commit a785548)

Author: aescolar

include/zephyr/bluetooth/services/cts.h

@@ -16,7 +16,6 @@
  */
 
 #include <stdint.h>
-#include <zephyr/posix/time.h>
 
 #ifdef __cplusplus
 extern "C" {

subsys/bluetooth/services/cts.c

@@ -7,9 +7,17 @@
  *
  * SPDX-License-Identifier: Apache-2.0
  */
+
+#undef _POSIX_C_SOURCE
+#define _POSIX_C_SOURCE 200809L /* To get gmtime_r()'s prototype */
+
+#ifdef CONFIG_BT_CTS_HELPER_API
+#include <time.h>
+#include <zephyr/sys/timeutil.h>
+#endif
+
 #include <stdbool.h>
 #include <zephyr/sys/byteorder.h>
-#include <zephyr/posix/time.h>
 
 #include <zephyr/bluetooth/conn.h>
 #include <zephyr/bluetooth/gatt.h>
@@ -26,9 +34,6 @@ static const struct bt_cts_cb *cts_cb;
 
 #ifdef CONFIG_BT_CTS_HELPER_API
 
-#include <time.h>
-#include <zephyr/sys/timeutil.h>
-
 int bt_cts_time_to_unix_ms(const struct bt_cts_time_format *ct_time, int64_t *unix_ms)
 {
 	struct tm date_time;