Deprecate specialized file errors in OutputPage and fix escaping

Deprecate specialized file errors in OutputPage and fix escaping

OutputPage has a number of specialized error reporting methods
related to file handling. With exception of showFileDeleteError,
they are all unused. In my opinion such specialized error handling
does not belong in OutputPage, but in whatever class is generating
the error.

Futhermore, these functions do not appropriately escape their
arguments or their i18n messages. I replaced the one usage
in SpecialUpload with an equivalent that does escape properly.
This is not exploitable as the attacker is not in control of
the temporary file name, but it is very bad practice.

This deprecates the following methods:
* OutputPage::showFileDeleteError()
* OutputPage::showFileNotFoundError()
* OutputPage::showFileRenameError()
* OutputPage::showFileCopyError()
* OutputPage::showUnexpectedValueError()

[Discovered with the help of an experimental phan plugin]

Change-Id: I9e7aaa59ded66f32c78cfdfed1e59e073ffd5051