Revert "Feature - Adds UpgradeableLoaderInstruction::Migrate (#4661)"

[joncinque]

Problem

#4661 introduced a change to the loader-v3 instruction after the v2.2 branch was cut, which means that we currently cannot remove the sdk from agave with #4867

Summary of Changes

Revert commit 11dfda5.

[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.

[willhickey]

Approved, since this will unblock removing the SDK.