Remove the dependency to deprecated gettext-extractor package

[joelit]

Reasons for creating this PR

This PR removes the dependency to twig-gettextExtractor, as it is a package no longer maintained

Link to relevant issue(s), if any

• Closes Updating twig-gettext extractor (and possibly changes for translating Finnish, Swedish and English UI) #1153

Known problems or uncertainties in this PR

This PR will not get rid of related and abandoned twig-extensions package, as it is used by the twig translation filters in Skosmos. There is a separate issue of that in #1247

Checklist

• phpUnit tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works (if not, explain why below)
• The PR doesn't introduce unintended code changes (e.g. empty lines or useless reindentation)

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
No Duplication information

[codecov]

Codecov Report

Merging #1257 (d686d6e) into master (e7f3bef) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master    #1257   +/-   ##
=========================================
  Coverage     68.85%   68.85%           
  Complexity     1627     1627           
=========================================
  Files            32       32           
  Lines          3994     3994           
=========================================
  Hits           2750     2750           
  Misses         1244     1244           

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[kinow]

Looks good to me. No code updated, so I assume it was not in use. CI green so shouldn't break anything I guess.

[osma]

There is also a static, modified copy of twig-gettext-extractor under tools/twig-gettext-extractor. If we want to excise it completely, that should probably be removed too (which would also remove the tools directory as it's the only file there).