Remove the unused env parameter from a2p's main, and the associated pragma.

a2p's main has had the traditional Unix third parameter (env) forever.
Commit 24801a4b9a14a562 in May 2005 increased the strictness of the Tru64
compiler, and added pramgas where necessary to counter its warnings.
However, a2p's main doesn't actually *use* the env parameter, so a better
solution is to remove it. Which means that the pragma can be removed too.