[CodingStyle] Deprecate BinaryOpStandaloneAssignsToDirectRector

[TomasVotruba]

Deprecates BinaryOpStandaloneAssignsToDirectRector.

The rule only fires on a very narrow shape - a method/function/closure with exactly 3 statements: 2 standalone variable assigns followed by a return with a binary op comparing those 2 variables. Outside that shape it does nothing, and inlining named variables into the comparison often makes the code less readable, not more. The purpose is unclear.

 function run()
 {
-    $value = 100;
-    $anotherValue = 200;
-
-    return $value <=> $anotherValue;
+    return 100 <=> 200;
 }

Removed from the CodingStyleLevel set, tests dropped, and the now-unused VariableAndExprAssign value object removed.