server: Remove ->argc, ->argv from struct command_context.

server: Remove ->argc, ->argv from struct command_context.

Command handlers should not look at the argv[] vector directly
but only use the lopsub library functions to access the parsed
command line.

In fact, the only function which accesses the argv vector is
run_command(). Defining argc and argv as local variables in this
function allows to drop the two members from the command context
structure.