PSR12/ReturnTypeDeclaration: remove redundant conditions

The `isset()`'s in the same condition block already take care of this.

Author: jrfnl

src/Standards/PSR12/Sniffs/Functions/ReturnTypeDeclarationSniff.php

@@ -47,8 +47,6 @@ public function process(File $phpcsFile, $stackPtr)
 
         if (isset($tokens[$stackPtr]['parenthesis_opener']) === false
             || isset($tokens[$stackPtr]['parenthesis_closer']) === false
-            || $tokens[$stackPtr]['parenthesis_opener'] === null
-            || $tokens[$stackPtr]['parenthesis_closer'] === null
         ) {
             return;
         }