Tidy-up dependency checking in configure

Don't support any packaging of dose.common or dose.algo and re.glob
doesn't need explicitly checking. extlib is no longer used by opam.

configure.ac

@@ -322,19 +322,20 @@ AC_SUBST(CONF_MANIFEST_O)
 
 echo
 
+# Dependencies
 AC_CHECK_OCAML_PKG([unix])
 AC_CHECK_OCAML_PKG([bigarray])
-AC_CHECK_OCAML_PKG([extlib])
 AC_CHECK_OCAML_PKG([re])
-AC_CHECK_OCAML_PKG([re.glob])
 AC_CHECK_OCAML_PKG([base64])
 AC_CHECK_OCAML_PKG([cmdliner])
 AC_CHECK_OCAML_PKG([ocamlgraph])
 AC_CHECK_OCAML_PKG([cudf])
-AC_CHECK_OCAML_PKG(dose3.common,dose.common)
-AC_CHECK_OCAML_PKG(dose3.algo,dose.algo)
+AC_CHECK_OCAML_PKG([dose3.common])
+AC_CHECK_OCAML_PKG([dose3.algo])
 AC_CHECK_OCAML_PKG([opam-file-format])
 AC_CHECK_OCAML_PKG([spdx_licenses])
+
+# Optional dependencies
 AC_CHECK_OCAML_PKG([mccs])
 AC_CHECK_OCAML_PKG([opam-0install-cudf])
 
@@ -381,13 +382,6 @@ AS_IF([test "x$OPAM_0INSTALL_SOLVER_ENABLED" = "xtrue" -a "x$OCAML_PKG_opam_0ins
   ])
 ])
 
-dnl echo
-dnl echo "extlib........................ ${OCAML_PKG_extlib}"
-dnl echo "re............................ ${OCAML_PKG_re}"
-dnl echo "cmdliner...................... ${OCAML_PKG_cmdliner}"
-dnl echo "graph......................... ${OCAML_PKG_ocamlgraph}"
-dnl echo "cudf.......................... ${OCAML_PKG_cudf}"
-dnl echo "dose3......................... ${OCAML_PKG_dose3}"
 echo
 
 AS_IF([test "x${enable_checks}" != "xno" && {
@@ -398,6 +392,7 @@ AS_IF([test "x${enable_checks}" != "xno" && {
        test "x$OCAML_PKG_ocamlgraph" = "xno" ||
        test "x$OCAML_PKG_cudf" = "xno" ||
        test "x$OCAML_PKG_dose3_common" = "xno" ||
+       test "x$OCAML_PKG_dose3_algo" = "xno" ||
        test "x$OCAML_PKG_opam_file_format" = "xno" ||
        test "x$OCAML_PKG_spdx_licenses" = "xno" ||
        test "x$CPPO" = "x" ||