Fix the issues reported by phpcs

Problem/Motivation

Getting following warnings.

FILE: /var/www/html/modules/contrib/taxonomy_bootstrap_accordion/src/Plugin/Block/TaxonomyMenuBlock.php
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FOUND 0 ERRORS AND 4 WARNINGS AFFECTING 4 LINES
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131 | WARNING | Vocabulary::loadMultiple calls should be avoided in classes, use dependency injection instead
134 | WARNING | Unused variable $machine.
154 | WARNING | Vocabulary::load calls should be avoided in classes, use dependency injection instead
224 | WARNING | Vocabulary::loadMultiple calls should be avoided in classes, use dependency injection instead
---------------------------------------------------------------------------------------------------------------

Time: 729ms; Memory: 6MB

Steps to reproduce

Run following command

phpcs --standard=Drupal,DrupalPractice --extensions=php,module,inc,install,test,profile,theme,css,info,txt,md,yml modules/contrib/taxonomy_bootstrap_accordion/

Proposed resolution

Above warnings need to be fixed.