RSA1_5 cleanup

[peppelinux]

as @rohe exposed in #88 (comment)

A quick search also reveals RSA1_5 in a couple of tests and in src/cryptojwt/jwt.py and src/cryptojwt/jwk/wrap.py .
We can replace i tests but changing jwt.py and wrap.py is trickier. That could easily be a breaking change.

[peppelinux]

Could we consider that the following PRs
#86
#89
closes this issue?

[rohe]

Yes !