import re
s = "https://content-available-to-author-only.com/wall505680146_2821,id505680146,социальные сети"
print( re.sub(r"https?://[^,\s]+,?", "", s) )
aW1wb3J0IHJlCnMgPSAiaHR0cHM6Ly9jb250ZW50LWF2YWlsYWJsZS10by1hdXRob3Itb25seS5jb20vd2FsbDUwNTY4MDE0Nl8yODIxLGlkNTA1NjgwMTQ2LNGB0L7RhtC40LDQu9GM0L3Ri9C1INGB0LXRgtC4IgpwcmludCggcmUuc3ViKHIiaHR0cHM/Oi8vW14sXHNdKyw/IiwgIiIsIHMpICk=