WASM: Simplify `Host_funcs.base_V4` definition

Context

As of now, [base_V4] is strictly equal to [base_V3], but while not incorrect,
the current definition of [base_V4] consists in adding a second time the host
function introduced in the third revision of the PVM. The resulting [Registry]
is equal, because adding the same entry twice is equivalent to adding it once,
but that’s not ideal.

This patch fixes this, and define [base_V3] as an alias for [base_V3].

Manually testing the MR

CI should prevail.

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).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR