PipeWriteType: put it back as an empty class generating error for any use

During tests of 10.1.0rc1 with Bliss we found out, that PoGo generated servers breaks due to they always import PipeWriteType, even it is not used.

So now all PoGo generated servers will break with 10.1. I propose, that we replace PipeWriteType Enum with dummy class, which can be imported, but at any attemts to be used generates error.

PS @dlacoste-esrf: anyway it will be good in future releases of PoGo not to import PipeWriteType at all