platform_util: Centralize deprecation

Update all files containing MBEDTLS_DEPRECATED to use the definition
from platform_util.h. This avoids duplication across multiple modules
and makes the code easier to read, understand, and maintain.
diff --git a/include/mbedtls/bignum.h b/include/mbedtls/bignum.h
index 0b26727..fc0958e 100644
--- a/include/mbedtls/bignum.h
+++ b/include/mbedtls/bignum.h
@@ -30,6 +30,8 @@
 #include MBEDTLS_CONFIG_FILE
 #endif
 
+#include "mbedtls/platform_util.h"
+
 #include <stddef.h>
 #include <stdint.h>
 
@@ -888,11 +890,6 @@
                          const mbedtls_mpi *N );
 
 #if !defined(MBEDTLS_DEPRECATED_REMOVED)
-#if defined(MBEDTLS_DEPRECATED_WARNING)
-#define MBEDTLS_DEPRECATED      __attribute__((deprecated))
-#else
-#define MBEDTLS_DEPRECATED
-#endif
 /**
  * \brief          Perform a Miller-Rabin primality test with error
  *                 probability of 2<sup>-80</sup>.
@@ -915,7 +912,6 @@
 MBEDTLS_DEPRECATED int mbedtls_mpi_is_prime( const mbedtls_mpi *X,
                           int (*f_rng)(void *, unsigned char *, size_t),
                           void *p_rng );
-#undef MBEDTLS_DEPRECATED
 #endif /* !MBEDTLS_DEPRECATED_REMOVED */
 
 /**