The ESourceRegistry can still be obtained from the EClientCache:
client_cache = e_composer_header_table_ref_client_cache (table);
registry = e_client_cache_ref_registry (client_cache);
...
g_object_unref (client_cache);
g_object_unref (registry);
Added functions:
e_composer_header_table_ref_client_cache()
Removed functions:
e_composer_header_table_get_registry()
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