Revert "configure.ac: Don't use pkg-config to search for libusb-1.0 on FreeBSD"

This reverts commit d0c10b78be.

Rollback breakage.

configure.ac

@@ -346,15 +346,7 @@ AM_CONDITIONAL([HAVE_LIBUDEV], [test x$libudev != xno])
 PKG_PROG_PKG_CONFIG()
 
 if test "x$ztex" != xno; then
-  case $target in
-    *-*-freebsd*)
-      LIBUSB_LIBS="-lusb"
-      LIBUSB_CFLAGS=""
-      ;;
-    *)
   PKG_CHECK_MODULES(LIBUSB, libusb-1.0, [AC_DEFINE(HAVE_LIBUSB, 1, [Define if you have libusb-1.0])], [AC_MSG_ERROR([Could not find usb library - please install libusb-1.0])])
-      ;;
-  esac
   USB_LIBS="$LIBUSB_LIBS"
   USB_FLAGS="$LIBUSB_CFLAGS"
 fi