configure.ac: remove AC_CHECK_FILE

The use of AC_CHECK_FILE and AC_CHECK_FILES cause the following error
when cross-compiling:

  configure: error: cannot check for file existence when cross compiling

The solution is to check for the file directly instead of using a macro.

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>

configure.ac

@@ -1515,8 +1515,9 @@
     ruledirprefix="$sysconfdir"
 
     if test "$enable_suricata_update" = "yes"; then
-      AC_CHECK_FILE([$srcdir/suricata-update/setup.py], [
-          have_suricata_update="yes"], [])
+        if test -f "$srcdir/suricata-update/setup.py"; then
+          have_suricata_update="yes"
+	fi
     fi
 
     if test "$have_suricata_update" = "yes"; then
@@ -2437,10 +2438,8 @@ fi
     AC_SUBST([RUSTUP_HOME_PATH], [$rustup_home_path])
     AC_SUBST([rustup_home])
 
-    if test "x$cross_compiling" != "xyes"; then
-      AC_CHECK_FILES([$srcdir/rust/vendor], [have_rust_vendor="yes"])
-    else
-      AS_IF([test -d "$srcdir/rust/vendor"], have_rust_vendor="yes", [])
+    if test -f "$srcdir/rust/vendor"; then
+      have_rust_vendor="yes"
     fi
 
     if test "x$have_rust_vendor" = "xyes"; then