Revert mb_trim to trim for broader PHP support

[veewee]

Reverts mb_trim changes in #91.

This was introduced by cs-fixer, but is only available in PHP 8.4+ (https://www.php.net/releases/8.4/en.php), resulting in fatal errors on lower versions.

(Sorry :-) )

[kernusr]

How did the tests pass with this?

[veewee]

I assume those code-paths are currently not covered by any tests.

[kernusr]

I checked — the code is covered by tests. However, during test execution, dev dependencies are installed, including symfony/polyfill-mbstring, which helps the tests pass.

> composer why symfony/polyfill-mbstring
friendsofphp/php-cs-fixer v3.87.1 requires symfony/polyfill-mbstring (^1.33) 
symfony/console           v7.3.3  requires symfony/polyfill-mbstring (~1.0)  
symfony/filesystem        v7.3.2  requires symfony/polyfill-mbstring (~1.8)
symfony/string            v7.3.3  requires symfony/polyfill-mbstring (~1.0)