Revert "doxygen: Update for Mbed Crypto"

This reverts commit 32577734e2635da3684d03ad04ba07044775cef9.
diff --git a/doxygen/mbedtls.doxyfile b/doxygen/mbedtls.doxyfile
index 2b14a36..4732271 100644
--- a/doxygen/mbedtls.doxyfile
+++ b/doxygen/mbedtls.doxyfile
@@ -1618,6 +1618,7 @@
                          P2MP \
                          P2MP_SERVER \
                          USE_CRYPTO \
+                         USE_SSL \
                          ENABLE_PLUGIN \
                          ENABLE_MANAGEMENT \
                          ENABLE_OCC \