Removes some unnecessary ternary conditionals

Removes some unnecessary ternary conditionals

In .../src/gromacs/mdlib/minimize.cpp calls to
the evaluate_energy() function.

Details:

The gmx_global_stat_t type argument in calls to
evaluate_energy() use this ternary expression:

evaluate_energy(..., gstat ? gstat : NULL, ...);

However, .../src/gromacs/legacyheaders/sim_util.h
shows gmx_global_stat_t is a typedef equivalent
to struct gmx_global_stat*, a pointer type; since
a pointer is TRUE if and only if it is not NULL,
the following is equivalent:

evaluate_energy(..., gstat, ...);

This patch performs this substitution.

Change-Id: I5bfc50dd8927fe1e797e06144535f61731fb7eb1