fix variable_info.cpp

variable_as_array_h::operator() expects the range to be passed as a pair (startindex, endindex). We accidentally passed the range as (startindex, size) instead.

Shadowm reported bugs related to global variables but most likely this can also lead to segfaults in other situations (some uses of [set_variables]).
remove check for "human_ai"

"human_ai" doesnt exist anymore so we can remove this check.
don't generate "user_description" on the host

the host it not capable to generate strings in the correct language.
("(Reserved for $playername)" was resolved on the host). Instead we now
generate the description on the clients.