don't create blank attributes in replay.cpp
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remove old server compability code

the code that was previously outcommented was outcommented for 1.11.13
compability.

we shouldn't always allow "global_variable", "global_vaiable" falls into
the "dependent" category and should only be allowed if we have a
"from_side" attribute.
only allow "dependent" commands for players

previously this was also allowed for teh host regardless whether he is a
player or not.
refactor wesnothd::game::is_legal_command
check "from_side" in wesnothd::game::is_legal_command

previously this was done outside of is_legal_command becasue
is_legal_command wasn't applied to the currently active side.
fixup a comment