build: remove --disable-rebuilds

It's unused and was only useful when perl wasn't installed. But perl is
a dependency of glib these days, so it's useless.

configure.ac

@@ -251,10 +251,6 @@ AC_ARG_ENABLE(debug,
                               [turn on debugging @<:@default=debug_default@:>@])],,
               [enable_debug=debug_default])
 
-AC_ARG_ENABLE(rebuilds,
-              [AS_HELP_STRING([--disable-rebuilds],
-                              [disable all source autogeneration rules])],,
-              [enable_rebuilds=yes])
 AC_ARG_ENABLE(installed_tests,
               AS_HELP_STRING([--enable-installed-tests],
                              [Install test programs (default: no)]),,
@@ -547,14 +543,6 @@ AM_CONDITIONAL(DISABLE_EXPLICIT_DEPS, test $enable_explicit_deps = no)
 
 AC_PATH_PROGS(PERL, perl5 perl)
 
-REBUILD=\#
-if test "x$enable_rebuilds" = "xyes" && \
-     test -n "$PERL" && \
-     $PERL -e 'exit !($] >= 5.002)' > /dev/null 2>&1 ; then
-  REBUILD=
-fi
-AC_SUBST(REBUILD)
-
 AC_CHECK_FUNCS(lstat mkstemp)
 AC_CHECK_FUNCS(localtime_r)