Useless ext-json requirement

[garak]

Since PHP 8.0 the JSON extension is bundled in the source code and it's not possible to disable it anymore.

[acelaya]

Thanks, I'll remove it, but it won't really make a difference 😅

> composer why ext-json 
Package "ext-json *" found in version "8.4.11".
shlinkio/shlink               dev-develop requires ext-json (*) 
devizzent/cebe-php-openapi    1.1.4       requires ext-json (*) 
geoip2/geoip2                 v3.3.0      requires ext-json (*) 
guzzlehttp/guzzle             7.10.0      requires ext-json (*) 
justinrainbow/json-schema     6.6.4       requires ext-json (*) 
matomo/matomo-php-tracker     3.4.0       requires ext-json (*) 
maxmind/web-service-common    v0.11.0     requires ext-json (*) 
mezzio/mezzio-problem-details 1.18.0      requires ext-json (*) 
nikic/php-parser              v5.7.0      requires ext-json (*) 
pagerfanta/core               v3.8.0      requires ext-json (*) 
phpunit/phpunit               12.5.4      requires ext-json (*) 
shlinkio/shlink-importer      9999999-dev requires ext-json (*) 
shlinkio/shlink-json          9999999-dev requires ext-json (*) 
spiral/goridge                4.2.1       requires ext-json (*) 
spiral/roadrunner-cli         v2.7.2      requires ext-json (*) 
spiral/roadrunner-http        v3.6.0      requires ext-json (*) 
spiral/roadrunner-jobs        v4.7.0      requires ext-json (*) 
spiral/roadrunner-worker      v3.6.2      requires ext-json (*) 

[garak]

Of course, the libraries that support PHP 7 still need the requirement.