cmake: Do not enable languages on behalf of consumers

Created by: bradking

Since #1176, our CMake package configuration file makes enable_language({C,CXX,Fortran}) calls on behalf applications using find_package(ADIOS2). This causes such applications to require a Fortran compiler even if they do not themselves use Fortran or link to any ADIOS2 Fortran binding libraries.

Remove the enable_language() calls from our package configuration file. Applications should enable whatever languages they are using. If any problem the enable_language() calls were addressing comes up again, we can consider other solutions. EDIT: Filter our own usage requirements to avoid referencing languages that are not enabled by the application.

Fixes: #1885

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