schema files have problematic top level "$ref" definitions

[kbroch-rivosinc]

Its unclear to me why we want these top level "$ref":

~/rvi/repos/riscv-software-src/riscv-unified-db on main                                                                                                           Py 3.12.4 at 05:14:11 PM
❯ jq -r 'select(has("$ref")) | ."$ref"' schemas/*_schema.json

#/$defs/csr_register
#/$defs/ext_data
#/$defs/inst_data