MAINTAINERS: Update entry for rtl8187

As Herton Ronaldo Krzesinski is no longer active, remove him as maintainer
for rtl8187.

The git tree entry is also removed.

Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Link: https://lore.kernel.org/r/20230804222438.16076-2-Larry.Finger@lwfinger.net
Signed-off-by: Johannes Berg <johannes.berg@intel.com>