Do not directly use AC_CANONICAL_SYSTEM from configure.ac

The macro is only needed because of DPKG_ARCHITECTURE which it already
requires.

configure.ac

@@ -6,7 +6,6 @@ AC_CONFIG_SRCDIR([lib/dpkg/dpkg.h])
 AC_CONFIG_MACRO_DIR([m4])
 AC_CONFIG_AUX_DIR([config])
 
-AC_CANONICAL_SYSTEM
 AC_GNU_SOURCE
 DPKG_ARCHITECTURE