Revert "configure.ac: FreeBSD can't use pkg-config to find libusb-1.0"

This reverts commit 4e706162c7.

configure.ac

@@ -353,11 +353,6 @@ if test "x$ztex" != xno; then
       LIBUSB_CFLAGS="-IC:/MinGW/include/libusb-1.0"
       AC_DEFINE(HAVE_LIBUSB, 1, [Define if you have libusb-1.0])
       ;;
-    *-*-freebsd*)
-      LIBUSB_LIBS="-lusb"
-      LIBUSB_CFLAGS=""
-      AC_DEFINE(HAVE_LIBUSB, 1, [Define if you have libusb-1.0])
-      ;;
     *)
       PKG_CHECK_MODULES(LIBUSB, libusb-1.0, [AC_DEFINE(HAVE_LIBUSB, 1, [Define if you have libusb-1.0])], [AC_MSG_ERROR([Could not find usb library - please install libusb-1.0])])
       ;;