mac80211_hwsim: remove maximum TX power

This is too low, at least ETSI regulatory domain would
allow 36 dBm on 5 GHz in (some? most?) cases. But there's
no reason hwsim should have a limit at all, so remove it.

See also
https://lore.kernel.org/r/20191108152013.13418-1-ramonreisfontes@gmail.com



Change-Id: I6edf81d2e82bc8ce7baa40bfc0f210b7b56ef275
Reported-by: Ramon Fontes <ramonreisfontes@gmail.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>