symlinks /usr/bin/python to the DEPRECATED python2

 In Ubuntu, all python packages use explicit python3 or python2
 interpreter and do not use unversioned /usr/bin/python at all. Some
 third-party code may still be python2 based, yet may use
 /usr/bin/python.
 .
 This is a convenience package which ships a symlink to point
 /usr/bin/python interpreter at the current default python2. It may
 improve compatibility with obsolete 3rd-party software, whilst
 breaking some modern software.
 .
 This package will be installed upon upgrades to Ubuntu 20.04, if
 DEPRECATED python2 was installed.
 .
 python2 is DEPRECATED and will not be provided in the future Ubuntu
 release. It is recommended to remove python2 and this package after
 ensuring that only python3 is in use.
 .
 No packages may declare dependencies on this package.