Remove false claim of dirname parameter from Folder::remove doc comment

[per1234]

Previously the documentation comment claimed the function had a dirname parameter even though the function does not have any parameters.

This only fixes the comment, leaving the incorrect information in the API docs:

Arduino_UnifiedStorage/docs/api.md

Lines 203 to 212 in 7fd805e

	### `remove` <a id="class_folder_1aca893daac6c6747895d50987cf9cf34c" class="anchor"></a>
	```cpp
	public bool remove()
	```
	Removes a directory.
	#### Parameters
	* `dirname` The name of the directory to remove.

That should be resolved by regenerating the documentation from the source code.

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Originally reported at f77f873#r145141720