Revert "Restore accidentally deleted data field from raw message."

This reverts commit e4a78ec9935af3b19d314e88b0ed935789162ca8.
Revert "Switch back to many subtypes for binary messages."

This reverts commit 3e954ea9c44bdd00b39d3f0d2cc43662e633c891.
Minimize the number of separate protobuf types.