Update CMake to build under library

[mattjala]

Depends on the changes to CMakeVOL.cmake from HDFGroup/hdf5#3450

• REST VOL must now be built at library build time with CMake, as described in the README
• Removed build scripts, autotools files, and PREBUILT_HDF5_DIR options.
• Removed hdf5 and vol-tests submodules (recent additions and outstanding PRs to vol-tests will need to get merged to HDF5's API tests).
• CI workflow now uses ctest to run the test_rest_vol file with valgrind.
• README describes updated build process