get_file_data() PHPDoc improvements

[hakre]

A parameter is named that does not exists. The function description contains information that is clear anyway (e.g. that a file will be opened for reading) or even wrong (that the function will load 1 or 2 kiB while it loads 8kiB).

Just ran over it and was in a mood of a quick patch.

Replying to ocean90:
Ah, there it is. I was sure that there is a component but did not see it on creation.

(In [16741]) Fix up the PHPdoc for get_file_data(). props hakre. fixes #14071

• @param array $default_headers array of regular expressions keyed with a fieldname, e.g. <code>array('Name' => 'Plugin Name')</code>

This is wrong. It's not an array of regular expressions, but of plain strings - preg_quote() is used on them.

[16828]