Fix prepare_ssl.py for OpenSSL 1.0.2a builds without Perl (using old system).

This change affects the makefiles checked into svn.python.org, which the 3.5
build no longer uses.  3.4 and 2.7 both still use those makefiles, but their
build_ssl.py scripts don't require an update; if the script is running the
'fix_makefiles' method it already has Perl available anyway.