Revert - Feature gate of disable_new_loader_v3_deployments

[Lichtso]

Problem

See #5189. Because this feature is activated by default in the test validator, lots of dApp devs have trouble because the CLI program subcommand only throws an error message and does not automatically forward to the replacement program-v4 subcommand. Doing this forwarding turned out much more challenging than originally anticipated, so I decided to remove this feature gate until we have the changes in the CLI ready.

Summary of Changes

Partial revert of #4666. The feature set part will stay as it currently resides in the SDK repository and the feature gate will be added back in later anyway.

[mergify]

The Firedancer team maintains a line-for-line reimplementation of the
native programs, and until native programs are moved to BPF, those
implementations must exactly match their Agave counterparts.
If this PR represents a change to a native program implementation (not
tests), please include a reviewer from the Firedancer team. And please
keep refactors to a minimum.

[mergify]

Backports to the beta branch are to be avoided unless absolutely necessary for fixing bugs, security issues, and perf regressions. Changes intended for backport should be structured such that a minimum effective diff can be committed separately from any refactoring, plumbing, cleanup, etc that are not strictly necessary to achieve the goal. Any of the latter should go only into master and ride the normal stabilization schedule. Exceptions include CI/metrics changes, CLI improvements and documentation updates on a case by case basis.