Essential dynamics: fixed legend in ED .xvg output file

If one performs flooding only and none of the standard essential dynamics
protocols are turned on, the .xvg output file did still print ED legends.
I moved the bNeedDoEdsam check from init_edi() to write_edo_legend(), so
that already here we can check whether ED or only flooding is performed.

Change-Id: Ic3a784b63b335059c17aed852d1b4a4f3126841a
Merge "Essential dynamics: fixed legend in ED .xvg output file" into release-4-6