FindHDF5: Remove unnecessary de-duplication of HDF5_LIBRARIES and friends

Reasons include:

• When both debug and optimized libraries are found, the corresponding keywords were getting de-duplicated and breaking.
• CMake's link line generation de-duplicates in many cases anyway.
• Other find modules do not explicitly de-duplicate in general.

Fixes: #21670 (closed)
Topic-rename: FindHDF5-no-dedup-keywords