Update copyright headers/footers

[mlieberman85]

Based on ossf/tac#485 it looks like there might be new guidance on what the copyrights should look like. Right now they include years for example

[funnelfiasco]

Ack. I'll wait to act on this until we have guidance from LF Legal. Removing the year makes sense, but the points raised in the Slack conversation about "GUAC a Series of LF Projects, LLC" versus something like "GUAC contributors" are reasonable. I have subscribed to the TAC issue to follow this.