base: Drop do_package base definition

I can't see how anyone would be using this very old package function definition
since package.bbclass is always inherited in modern OE. All it seems to do
is waste CPU cycles. Drop it and it's associated EXPORT_FUNCTIONS entry.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>