Don't start docstrings with "This function" or similar

Don't start docstrings with "This function" or similar

* lisp/calculator.el (calculator-add-operators):
* lisp/erc/erc-backend.el (erc-server-ping-handler):
* lisp/erc/erc-log.el (erc-generate-log-file-name-with-date):
(erc-generate-log-file-name-short):
* lisp/erc/erc-track.el (erc-track-shorten-function):
* lisp/eshell/em-smart.el (eshell-where-to-jump):
* lisp/eshell/esh-mode.el (eshell-begin-on-new-line):
* lisp/gnus/gnus-art.el (gnus-prompt-before-saving):
* lisp/mail/supercite.el (sc-cite-region-limit):
* lisp/net/nsm.el (network-security-protocol-checks):
* lisp/org/org-element.el
(org-element--cache-avoid-synchronous-headline-re-parsing):
* lisp/progmodes/hideif.el (hif-merge-ifdef-region):
* lisp/progmodes/modula2.el (m2-indent):
* lisp/progmodes/xscheme.el (xscheme-running-p):
(xscheme-control-g-disabled-p):
* lisp/tab-bar.el (tab-bar--event-to-item):
* lisp/which-key.el (which-key--hide-popup): Don't start docstrings with
"This function" or "This variable".

(cherry picked from commit 186ea407326166ee4669ce6fe84871c1e16c657c)