Minor documentation and script cleanups (#6868)

* Remove mention of no longer used IRC network

Channels exist on matrix, and on libera.chat now.

* Correctly match only files with .png extension

The current search would match files such as 'createpng'.

* Fix comparison in script

The result was always false, due to comparing a literal string instead of a variable.

* Use correct license files from upstream

Correct license files obtained from:
https://www.gnu.org/licenses/old-licenses/gpl-2.0.txt
https://www.gnu.org/licenses/gpl-3.0.txt
https://www.gnu.org/licenses/old-licenses/lgpl-2.1.txt
https://www.gnu.org/licenses/lgpl-3.0.txt

* Refresh several shell scripts

This fixes several shellcheck warnings, as well as makes the code more
robust and have consistent codestyle between all the files.

* Trim excess whitespace

utils/keepassxc-kdewallet

@@ -4,10 +4,10 @@
 ### change the path to suit your installation or set KDBX_SEARCH before calling ###
 : ${KDBX_SEARCH:=~/.KeePass/*.kdbx}
 
-PROG="${0##*/}"
+PROG=${0##*/}
 KEEPASSXC=$(which -a keepassxc | sed -e "\\,$0,d" -e 'q')
 
-function daemon_main {
+daemon_main() {
   # open kdewallet
   handle=$(qdbus org.kde.kwalletd5 /modules/kwalletd5 org.kde.KWallet.open kdewallet 0 "$PROG")
   while [[ true != $(qdbus org.kde.kwalletd5 /modules/kwalletd5 org.kde.KWallet.isOpen kdewallet) ]]; do
@@ -27,7 +27,7 @@ function daemon_main {
   qdbus org.kde.kwalletd5 /modules/kwalletd5 org.kde.KWallet.close "$handle" "false" "$PROG"
 }
 
-if [[ '-d' = "$1" ]]; then
+if [[ $1 == '-d' ]]; then
   exec >&~/tmp/$PROG.log
   set -vx
   daemon_main