turning off OpenMP after a configure pass results in link-time error
After configuring with default or manually set
GMX_OPENMP=ON, turning it off results in link time errors that complain about undefined references to OpenMP API functions.
Removed option to use OpenMP with the TNG library.
OpenMP was only used for compiling a few of the examples. With
the latest version of the TNG library the detection is done when
compiling those examples and skipping them if OpenMP is not