When FindHDF5 was first added in commit e6734068 (Add HDF5 find
module..., 2009-08-24) it contained a workaround for a bug in
SelectLibraryConfigurations that did not transform lists correctly.
That bug was fixed by commit 5797512c (SelectLibraryConfiguration:
generate correct output when input vars are lists, 2012-07-28).  Then
refactoring in commit 04d4dc33 (SelectLibraryConfigurations: Use
-NOTFOUND instead of copying the vars, 2013-07-08) changed undocumented
behavior on which the original workaround relied.  The result puts
entries like HDF5_hdf5_LIBRARY_DEBUG-NOTFOUND in HDF5_LIBRARIES.

Fix this by dropping the original workaround since the underlying issue
has been fixed anyway.  Use the HDF5_${LIB}_LIBRARY selected by the call
to select_library_configurations directly.