[TASK] Drop the unused ParserState::getCharset()

As this class is `@internal`, we do not need a deprecation
process for this.

Author: oliverklee

src/Parsing/ParserState.php

@@ -82,16 +82,6 @@ public function setCharset($sCharset): void
         }
     }
 
-    /**
-     * Returns the charset that is used if the CSS does not contain an `@charset` declaration.
-     *
-     * @return string
-     */
-    public function getCharset()
-    {
-        return $this->sCharset;
-    }
-
     /**
      * @return int
      */