Revert "Python: Warn old warpx.multifab Signature (#5326)"

[RemiLehe]

It seems that the changes of #5326 is causing confusion among some users.

With #5326, users typically receive a message saying that the "signature is deprecated" (which is actually incorrect ; this should say "will soon be deprecated"). As a consequence, users think that their simulation result is invalid (which is again incorrect ; using this signature is still fine for now), and try to change it according the printed instuctions, i.e.:

Please use:
- multifab('prefix', level=...) for scalar fields
- multifab('prefix', dir=..., level=...) for vector field components

But because there is no link to a concrete example or test, users typically try:

multifab("Efield_fp", dir=0, level=0)

and then get

TypeError: multifab(): incompatible function arguments. The following argument types are supported:
    1. (self: pywarpx.warpx_pybind_3d.WarpX, internal_name: str) -> amrex.space3d.amrex_3d_pybind.MultiFab
    2. (self: pywarpx.warpx_pybind_3d.WarpX, scalar_name: str, level: int) -> amrex.space3d.amrex_3d_pybind.MultiFab
    3. (self: pywarpx.warpx_pybind_3d.WarpX, vector_name: str, dir: pywarpx.warpx_pybind_3d.Direction, level: int) -> amrex.space3d.amrex_3d_pybind.MultiFab

I am guessing that most users will get stuck at this point.

The error message does suggest that the user has to create a Direction object, but since there is no example on how to create this, it is unlikely that most users will be able to overcome this issue.

I would suggest to temporarily revert #5326, and then re-introduce it with:

• updated instructions on how to create a Direction objects
• updated warning that says "will be deprecated" instead of "is deprecated".

[RemiLehe]

It seems that the example given here does not actually work.