Revert "Add checks for particles that are at same position, this isn't...

Revert "Add checks for particles that are at same position, this isn't allowed, and update the cell h_max to that of the particles after the initial ghost tasks have ran. This is needed before regridding if the h values of the particles in the IC are set to be smaller than reality (ends up looking like rebuilding failed as the particles are too far outside their cells)."

This reverts commit 3d12f382.