Cleanup: removed separate no-scrape marker file

Changed prefix file format to allow encoding of no-scrape request
using "# disabled" pseudo comment. Single automatic routing medata
file makes proper synchronization easier to implement and simplifies
overall implementation.

This also eliminated two HEAD requests per remote (due to a bug
original implementation performed HEAD no-scrape file for each
discovery strategy, not once per remote).

Signed-off-by: Igor Fedorenko <igor@ifedorenko.com>