Britney Spears is carrying on as if nothing happened ... spotted doing everyday errands like she didn’t just cash in one of the most iconic catalogs in pop history. The pop legend was seen deep in conversation on her phone while cruising in her Mercedes G63 AMG near her Thousand Oaks home in the L.A. area Thursday. Rocking shades and casual clothes, Britney kept it low-key during the solo outing -- all just days after TMZ broke the news she sold the rights to her music. BTW ... if you're