Generic/UnusedFunctionParameter: remove unused variable

I found this while working on improving code coverage for this sniff.
The value of this variable is defined again on line 112 and then only
used right below it on line 113
(https://github.com/PHPCSStandards/PHP_CodeSniffer/blob/84acf4e56f110db8e75cb9a575c5727df637643c/src/Standards/Generic/Sniffs/CodeAnalysis/UnusedFunctionParameterSniff.php#L112-L113)
so it should be safe to remove it.

Author: rodrigoprimo

src/Standards/Generic/Sniffs/CodeAnalysis/UnusedFunctionParameterSniff.php

@@ -94,7 +94,6 @@ public function process(File $phpcsFile, $stackPtr)
 
         $errorCode  = 'Found';
         $implements = false;
-        $extends    = false;
 
         if ($token['code'] === T_FUNCTION) {
             $classPtr = $phpcsFile->getCondition($stackPtr, T_CLASS);