reconsider ILINearby nowcast signal retrieval

[vpnagraj]

we have previously implemented some logic to handle missing signal from the ILINearby API (details in #159).

we should consider deprecating the get_nowcast_ili() function ... or at the very least updating the messaging with a more recent date / Github issue reference than what it returns now:

fiphde:::get_nowcast_ili()
#> Warning in fiphde:::get_nowcast_ili(): As of October 2022 ILInearby was no
#> longer being updated. This will likely return 'NA'. See
#> https://github.com/cmu-delphi/delphi-epidata/issues/993
#> The nowcast data returned is missing some or all of the query weeks. Returning NA.
#> [1] NA