v2.2: Revert - Feature gate of disable_new_loader_v3_deployments (backport of #5300)

[mergify]

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.

---

This is an automatic backport of pull request #5300 done by [Mergify](https://mergify.com).

[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.

[t-nelson]

making a release with this merged and the feature set not updated is going to create undetectable runtime incompatibilities with prior releases

[Lichtso]

Only once we re-add the feature, and by the time we should have the feature set back in the Agave repository.
Removing the logic of a feature gate in itself can not be rekeyed anyway.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 33.33333% with 2 lines in your changes missing coverage. Please review.

Project coverage is 83.4%. Comparing base (39ae42d) to head (596d023).

Additional details and impacted files

@@           Coverage Diff           @@
##             v2.2    #5315   +/-   ##
=======================================
  Coverage    83.3%    83.4%           
=======================================
  Files         805      805           
  Lines      371543   371526   -17     
=======================================
+ Hits       309816   309866   +50     
+ Misses      61727    61660   -67     

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[t-nelson]

@pgarg66 mind SMEing this one one last time?