ostree_kernel_args_delete_if_present checks if an argument is present
in OstreeKernelArgs and delete it.
Signed-off-by: Rafael Garcia Ruiz <rafael.garcia@collabora.com>
Check if an argument is present in OstreeKernelArgs. This is a way to
make easier idempotent append and delete operations.
ostree_kernel_args_append_if_missing uses it to avoid inserting a
duplicate key.
Closes#2329
Signed-off-by: Rafael Garcia Ruiz <rafael.garcia@collabora.com>