Remove unneeded metadata.xml files

[Bakual]

Currently, we have metadata.xml files in each view. However since Joomla 3.5.0 those are no longer required (PR #7654).

Summary of Changes

This PR removes the metadata.xml files since they have no function at all in core.
This will help extension developers to see best practices.

Testing Instructions

• Test creating menu items for the affected views. Nothing strange should happen.
• Check the menu item type text in the menu item manager, see picture. Nothing should change there.
  

Documentation Changes Required

None to my knowledge.

[photodude]

Documentation Changes Required Suggested

The Hello world example component code/development tutorial likely needs a major update to match with 3.5+ best practices like the removal of metadata.xml. (I think it was last revised with 3.2)

[Minei3oat]

I have tested this item ✅ successfully on bbbf934

I didn't found a posibility to test the views of com_mailto because there are no selectable views (XML-files are missing).
All other was working.

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[jsubri]

Should we have these files in script.php at the same time?

[brianteeman]

Yes

[Bakual]

I didn't add them to the script.php because it doesn't really matter if they are present or not. As you see currently 😄
If we merge something like this #10548, they may be needed again in special cases.

[brianteeman]

It starts to become a mess if you have some sites with files and some sites without. Especially security scanners. If the files are not needed then they should be removed

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[Bakual]

Added the files to the script.php. If it's not merged for 3.6.3 that files needs to be adjusted so the comment matches :)

[Bakual]

The Hello world example component code/development tutorial likely needs a major update to match with 3.5+ best practices like the removal of metadata.xml. (I think it was last revised with 3.2)

@photodude I had a look but couldn't find anything related to metadata.xml on a first glance. At least not where I would have expected it (https://docs.joomla.org/J3.x:Developing_an_MVC_Component/Adding_a_menu_type_to_the_site_part)

[brianteeman]

I have tested this item ✅ successfully on 5638ec2

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[zero-24]

RTC

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