Drop file_exists check for _FILE variables (#2234)

* Drop file_exists check for _FILE variables

A PHP warning is generated if the file does not exist.
Otherwise there is no indicator why the variable is not used.

Signed-off-by: J0WI <J0WI@users.noreply.github.com>

* fixup: typo in smtp.config.php

Signed-off-by: Josh <josh.t.richards@gmail.com>

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Signed-off-by: J0WI <J0WI@users.noreply.github.com>
Signed-off-by: Josh <josh.t.richards@gmail.com>
Co-authored-by: Josh <josh.t.richards@gmail.com>