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/md.h b/include/mbedtls/md.h
index 0b0ec91..0423e45 100644
--- a/include/mbedtls/md.h
+++ b/include/mbedtls/md.h
@@ -35,6 +35,8 @@
 #include MBEDTLS_CONFIG_FILE
 #endif
 
+#include "mbedtls/platform_util.h"
+
 #define MBEDTLS_ERR_MD_FEATURE_UNAVAILABLE                -0x5080  /**< The selected feature is not available. */
 #define MBEDTLS_ERR_MD_BAD_INPUT_DATA                     -0x5100  /**< Bad input parameters to function. */
 #define MBEDTLS_ERR_MD_ALLOC_FAILED                       -0x5180  /**< Failed to allocate memory. */
@@ -159,11 +161,6 @@
 void mbedtls_md_free( mbedtls_md_context_t *ctx );
 
 #if ! defined(MBEDTLS_DEPRECATED_REMOVED)
-#if defined(MBEDTLS_DEPRECATED_WARNING)
-#define MBEDTLS_DEPRECATED    __attribute__((deprecated))
-#else
-#define MBEDTLS_DEPRECATED
-#endif
 /**
  * \brief           This function selects the message digest algorithm to use,
  *                  and allocates internal structures.
@@ -183,7 +180,6 @@
  * \return          #MBEDTLS_ERR_MD_ALLOC_FAILED on memory-allocation failure.
  */
 int mbedtls_md_init_ctx( mbedtls_md_context_t *ctx, const mbedtls_md_info_t *md_info ) MBEDTLS_DEPRECATED;
-#undef MBEDTLS_DEPRECATED
 #endif /* MBEDTLS_DEPRECATED_REMOVED */
 
 /**