Update affinity checking for Intel compiler

Update affinity checking for Intel compiler

Since release 2013, the Intel compiler no longer sets
OpenMP affinity by default according to intel docs. This
means the code that tried to disable it by setting
environment variables no longer had any effect (and we
likely have not checked it the last few years). In
addition, it is not ideal behaviour in a library either to
assume that no other code has executed OpenMP prior to a call
or to set environment variables that influence other code
execution too. However, we will still disable Gromacs' own
thread affinity if it has been set by the user or calling code.

Change-Id: I57a952766e87a35483f1960b349f7c30d5b85f24