Deactivate default --better-errors to speed up RPC calls

Context

This MR deactivates the global --better-errors option in order to prevent the client from running expensive /describe/... RPC calls.

This significantly speeds up some of the tests. E.g. $ dune exec tezt/tests/main.exe -- -f RPC_test.ml --title "Oxford: (mode proxy) RPC tests: chain" goes from 2m45s to 15s on my laptop.

Manually testing the MR

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
• Document any change to the user interface, including configuration parameters (see node configuration)
• Provide automatic testing (see the testing guide).
• For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
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