Let sample_restraint CI tests get googletest sources
For -DDOWNLOAD_GOOGLETEST=ON
, update the CMake infrastructure per
https://google.github.io/googletest/quickstart-cmake.html#set-up-a-project.
Pin to the same googletest reference as main GROMACS project.
Reverts !2201 (merged) c016fbb4
Refs #4287 (closed)
Edited by M. Eric Irrgang