Remove unused NSE library requires

for lib in nselib/*.lua*; do l=${lib#*/}; l=${l%.lua*}; find . -name \
  \*.lua -o -name \*.nse | xargs grep -l "require .$l\>" | xargs grep \
  -c "\<$l\." | grep ':0$' | awk -F: '{print "'$l'", $1}'; done

Did not remove calls to stdnse.silent_require since these can be used to
abort script execution if OpenSSL is not included, even if the script
does not directly call openssl.* (perhaps it uses comm.tryssl instead,
for instance).

Also did not remove require "strict", since that library is special and
modifies the environment.

scripts/ip-forwarding.nse

@@ -2,7 +2,6 @@ local dns = require "dns"
 local nmap = require "nmap"
 local packet = require "packet"
 local stdnse = require "stdnse"
-local string = require "string"
 local ipOps = require "ipOps"
 
 description = [[