I just got about 40 can lights installed in my 40 year old house. Is it reasonable to ask the electrician to haul away all the trash and old fixtures that were removed?
Yes, it is reasonable to ask for disposal. And if it wasn't included in the quote, it is reasonable for him to charge you to do so.
I wouldn't be happy if after putting in 40 lights they wouldn't take the trash away.
Yes, an electrician should clean up after the work. May be a misunderstanding so just ask. The individual may have assumed you wanted the old fixtures.
However, as an alternative to displsal you may want to think about donating the old fixtures if they are in good condition. We recently redid the interior lighting on an early 1980's house and had numerous dated pendants, swags, table lamps and surface mounts. A small local charity was genuinely pleased with the donations. I made sure each piece had all the hardware needed and was ready to be used.