python-aiosignal: remove the package

python-aiosignal: remove the package

aiosignal is a small aio-libs helper that provides a Signal class for
fan-out of coroutine callbacks. Its only practical use is as a runtime
dependency of aiohttp, which is not packaged in this repository, and no
other package here declares aiosignal as a runtime or build dependency.

Drop the package; users who pull in aiohttp via pip on the target will
get aiosignal as a transitive dependency anyway.

Signed-off-by: Alexandru Ardelean <redacted>