Don't start docstrings with "This function"

Don't start docstrings with "This function"

* lisp/calculator.el (calculator-add-operators):
* lisp/erc/erc-log.el (erc-generate-log-file-name-with-date)
(erc-generate-log-file-name-short):
* lisp/eshell/esh-mode.el (eshell-begin-on-new-line):
* lisp/progmodes/hideif.el (hif-merge-ifdef-region):
* lisp/tab-bar.el (tab-bar--event-to-item):
* lisp/textmodes/artist.el (artist-no-rb-unset-point2)
(artist-no-rb-unset-points):
* lisp/which-key.el (which-key--hide-popup): Don't start function
docstrings with "This function".

(cherry picked from commit 4df832750c811abc5ccbe7bfcefe1ad8f144af8e)