Add new MatchArmRemoval mutator

[sidz]

This PR:

• Adds Add new MatchArmRemoval mutator
• Covered by tests
• Doc PR: Update mutators.md with MatchArmRemoval mutator site#243

Mutates:

match ($x) {
-   'cond1', 'cond2' => false,
+  'cond2' => false,
    2 => null,
    default => throw new \Exception(),
};

match ($x) {
-   'cond1', 'cond2' => false,
+  'cond1' => false,
    2 => null,
    default => throw new \Exception(),
};

match ($x) {
-   'cond1', 'cond2' => false,
    2 => null,
    default => throw new \Exception(),
};

match ($x) {
   'cond1', 'cond2' => false,
-    2 => null,
    default => throw new \Exception(),
};

match ($x) {
   'cond1', 'cond2' => false,
    2 => null,
-    default => throw new \Exception(),
};

[maks-rafalko]

👍 would you mind update the docs?

[sidz]

Done