Drop problematic configure check

This drops the configure-time check for the H5TS_mutex_lock function. It has two problems:

1. The function is not used anywhere in the code.
2. I understand that we would like to know whether HDF5 is built with the thread-safety feature enabled. However, the fact that we check the library and might even link to it is very well hidden from the user. There is no --with-hdf5 option, which could indicate that. The only way for the user to ensure the consistency of the check is to provide an extra -L linker flag via the LDFLAGS variable. Otherwise, it is very likely that the check runs against a wrong installation of HDF5, not the one that is actually used by the provided NetCDF library. The Libtool-generated *.la usually help with this problem, but those files are almost never installed nowadays.

I think that no information is better than wrong information. Hence, app/cdi.c does not report /threadsafe anymore. It also looks like the usage of the HAVE_NC4HDF5_THREADSAFE can be simply removed from src/stream.c.

We have another check that has the same 2. problem. It would be nice to get rid of it as well. The only source file where the result of the check is relevant is src/pio_server.c. Maybe Thomas can tell whether we can avoid using the H5get_libversion function.

This is not critical for ICON because those checks are suppressed when the library is configured as part of the model.

requested review from @m214003

changed the description