Simplify make_xkernel for xeus-lite

[JohanMabille]

The make_xkernel function should be simplified in xeus-lite 4.0 where we can break backward compatibility:

• the build_type should be removed
• The kernel loader should always pass the arguments from the kernel specs
• The interpreter constructor of the kernels should always accept arguments

[SylvainCorlay]

As discussed we will not address this for xeus-lite 4.0.

[JohanMabille]

Actually this cleanup requires changes in jupyterlite/xeus and in all xeus-based kernels first.