Fix compilation for cppyy-windows

[AlexisCompain]

Remove dllexport of deleted methods (clang_cl complains)

Is fixed by #28

[AlexisCompain]

Issue still present in version 3.2.3-r8

[goncaloalmeida]

Hello @AlexisCompain
we are checking your PR, in some internal tests we are with problems, which is why we did not take this or reject it yet.