www/e2guardian: Simplify Makefile

• Add USES=localbase instead of touching CFLAGS/CPPFLAGS
• Remove redundant localstatedir=/var from configure_ARGS, it's already passed by default mechanism

PR: 244437
Approved by: Marcello Coutinho <marcellocoutinho@gmail.com> (maintainer)
Sponsored by: Rubicon Communications, LLC (Netgate)