Add MBEDTLS_SELF_TEST check in header files

Add the `MBEDTLS_SELF_TEST` precompilation surrounding the self test functions,
which were missing this check in the header files. ( most of the header files were missing this check).
Addresses issue #971

include/mbedtls/sha1.h

@@ -304,6 +304,8 @@ MBEDTLS_DEPRECATED void mbedtls_sha1( const unsigned char *input,
 #undef MBEDTLS_DEPRECATED
 #endif /* !MBEDTLS_DEPRECATED_REMOVED */
 
+#if defined(MBEDTLS_SELF_TEST)
+
 /**
  * \brief          The SHA-1 checkup routine.
  *
@@ -317,6 +319,8 @@ MBEDTLS_DEPRECATED void mbedtls_sha1( const unsigned char *input,
  */
 int mbedtls_sha1_self_test( int verbose );
 
+#endif /* MBEDTLS_SELF_TEST */
+
 #ifdef __cplusplus
 }
 #endif