Revert "Allow application errors to be responded to requests"

This reverts commit 54f2bc511a2c7897303fc4e569b8cd7bbd188266.
bugfix: method_subtract error created nested jsonrpc_error_object

it is now the method's responsibility to create its own
jsonrpc_error_object on error. the only valid return values are 0 and -1.

there is no need for jsonrpc_error_object() function to take in a
user-supplied message. any user message could be supplied in the "data"
parameter. See method_subtract for an example.
add function jsonrpc_error_object_predefined()

we also revert jsonrpc_error_object() signature back to accepting "message" parameter.