Remove explicit link to MBEDTLS_CONFIG_FILE

This symbol is not declared in our code, so trying to explicitly
link to it causes a doxygen error.

Signed-off-by: Bence Szépkúti <bence.szepkuti@arm.com>
diff --git a/include/mbedtls/build_info.h b/include/mbedtls/build_info.h
index 625e926..c7d4cdb 100644
--- a/include/mbedtls/build_info.h
+++ b/include/mbedtls/build_info.h
@@ -4,7 +4,7 @@
  * \brief Build-time configuration info
  *
  *  Include this file if you need to depend on the
- *  configuration options defined in mbedtls_config.h or #MBEDTLS_CONFIG_FILE
+ *  configuration options defined in mbedtls_config.h or MBEDTLS_CONFIG_FILE
  */
  /*
   *  Copyright The Mbed TLS Contributors