release: adjust lang/python* dependencies for GCE

The lang/python3 port had failed to properly install because
it did in fact already exist and FORCE_PKG_REGISTER was not
set. So, behaviorally everything here was correct. However,
installing lang/python3 is in fact not correct and not needed,
so only install the lang/python port to provide symbolic links.

PR: 272354
MFC after: 3 days
MFC with: 510fd83138001b0a6e45b3fa6a7249377f806171
MFC with: cd8cad0ef5cd534dc7ae1dd9a470cac2057ed957
MFC with: 0ed426276fd52e917506ab87c05a61c6641ae298
Sponsored by: GoFundMe https://www.gofundme.com/f/gjbbsd