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/md4.h b/include/mbedtls/md4.h
index e7accd4..e101014 100644
--- a/include/mbedtls/md4.h
+++ b/include/mbedtls/md4.h
@@ -35,6 +35,8 @@
 #include MBEDTLS_CONFIG_FILE
 #endif
 
+#include "mbedtls/platform_util.h"
+
 #include <stddef.h>
 #include <stdint.h>
 
@@ -171,11 +173,6 @@
                                   const unsigned char data[64] );
 
 #if !defined(MBEDTLS_DEPRECATED_REMOVED)
-#if defined(MBEDTLS_DEPRECATED_WARNING)
-#define MBEDTLS_DEPRECATED      __attribute__((deprecated))
-#else
-#define MBEDTLS_DEPRECATED
-#endif
 /**
  * \brief          MD4 context setup
  *
@@ -240,7 +237,6 @@
 MBEDTLS_DEPRECATED void mbedtls_md4_process( mbedtls_md4_context *ctx,
                                              const unsigned char data[64] );
 
-#undef MBEDTLS_DEPRECATED
 #endif /* !MBEDTLS_DEPRECATED_REMOVED */
 
 /**
@@ -262,11 +258,6 @@
                      unsigned char output[16] );
 
 #if !defined(MBEDTLS_DEPRECATED_REMOVED)
-#if defined(MBEDTLS_DEPRECATED_WARNING)
-#define MBEDTLS_DEPRECATED      __attribute__((deprecated))
-#else
-#define MBEDTLS_DEPRECATED
-#endif
 /**
  * \brief          Output = MD4( input buffer )
  *
@@ -285,7 +276,6 @@
                                      size_t ilen,
                                      unsigned char output[16] );
 
-#undef MBEDTLS_DEPRECATED
 #endif /* !MBEDTLS_DEPRECATED_REMOVED */
 
 #if defined(MBEDTLS_SELF_TEST)