[Sync EN] Remove dead code in exec.xml example (#5705)

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Commit: https://github.com/php/doc-en/commit/462dddda87baa86fd760dcb1e3a0d2096e00a59b
PR: https://github.com/php/doc-en/pull/5705

Zu aktualisierende DE-Dateien

• reference/exec/functions/exec.xml