Remove expired ports:

2021-01-14 net-im/telegram: Upstream unmaintained; please migrate to
net-im/telegram-cli
2021-01-14 science/dlpoly-classic: MASTERSITE gone; possibly replaced by
https://gitlab.com/DL_POLY_Classic/dl_poly?
2021-01-15 security/py-gtts-token: Obsolete, please use audio/py-gtts instead

security/py-gtts-token: Deprecate port

* Since changes were made to Google's TTS API in November 2020 this port is no
  longer useful [1].

  [1] https://github.com/Boudewijn26/gTTS-token/blob/master/README.md

* The audio/py-gtts port has been adapted accordingly to the new API changes
  and has been updated in r559351 .

Drop python 2.7 support from a few ports

With hat:	portmgr

games/py-mnemosyne: Take Maintainer'ship, fix runtime error and add missing
dependencies

Latest version of games/py-mnemosyne requires new dependencies. This commit adds
the missing dependencies:

 - audio/py-gtts
 - security/py-gtts-token (required by audio/py-gtts)
 - textproc/py-googletrans

The games/py-mnemosyne port needs to be limited to Python 3.7+ to keep the
dependency chains intact. This is because textproc/py-googletrans depends on
www/py-httpx which is only for Python 3.7+.

PR:		247595
Submitted by:	kai
Reported by:	gspurki@gmail.com
Approved by:	tcberner (mentor)
MFH:		2020Q3
Differential Revision:	https://reviews.freebsd.org/D25895