These SPDX license identifiers are deprecated ([1]). Update them.

[1] https://spdx.org/licenses/

  sed \
     -e '1 s%^/\* SPDX-License-Identifier: \(GPL-2.0\|LGPL-2.1\)+ \*/$%/* SPDX-License-Identifier: \1-or-later */%' \
     -e '1,2 s%^\(--\|#\|//\) SPDX-License-Identifier: \(GPL-2.0\|LGPL-2.1\)+$%\1 SPDX-License-Identifier: \2-or-later%' \
     -i \
     $(git grep -l SPDX-License-Identifier -- \
         ':(exclude)shared/c-*/' \
         ':(exclude)shared/n-*/' \
         ':(exclude)shared/systemd/src' \
         ':(exclude)src/systemd/src')

  $ find * -type f |xargs perl contrib/scripts/spdx.pl
  $ git rm contrib/scripts/spdx.pl

  sed '1,3 { /^\(#\|--\) *vim:/d }; 1 { /^\/\* *vim:.*\*\/$/ d}' -i $(git grep -l 'vim:')

We no longer add these. If you use Emacs, configure it yourself.

Also, due to our "smart-tab" usage the editor anyway does a subpar
job handling our tabs. However, on the upside every user can choose
whatever tab-width he/she prefers. If "smart-tabs" are used properly
(like we do), every tab-width will work.

No manual changes, just ran commands:

    F=($(git grep -l -e '-\*-'))
    sed '1 { /\/\* *-\*-  *[mM]ode.*\*\/$/d }'     -i "${F[@]}"
    sed '1,4 { /^\(#\|--\|dnl\) *-\*- [mM]ode/d }' -i "${F[@]}"

Check remaining lines with:

    git grep -e '-\*-'

The ultimate purpose of this is to cleanup our files and eventually use
SPDX license identifiers. For that, first get rid of the boilerplate lines.

Correct the spelling across the *entire* tree, including translations,
comments, etc. It's easier that way.

Even the places where it's not exposed to the user, such as tests, so
that we learn how is it spelled correctly.