Drop `${CMAKE_DL_LIBS}` linkage from static cuFile (GDS) build

[jakirkham]

Currently we offer to build with cuFile (GDS) statically. However when we do that, we still link to ${CMAKE_DL_LIBS}, which supplies the behavior for dlopen to work. The dlopen logic only exists for the case where we dynamically to cuFile. Ideally we would drop this linkage in that case, this may require some code changes

Context - This came up in this thread: #905 (comment)