Block Editor: Remove custom justify format type in favor of Gutenberg

[danielbachhuber]

We currently have a 'Justify' option for paragraphs with this code:

wp-calypso/apps/wpcom-block-editor/src/default/features/rich-text.js

Lines 73 to 78 in 669b13b

	registerFormatType( 'wpcom/justify', {
	title: wpcomGutenberg.richTextToolbar.justify,
	tagName: 'p',
	className: null,
	edit: ConnectedRichTextJustifyButton,
	} );

After WordPress/gutenberg#48202 makes it to dotcom, we should remove our custom 'Justify' implementation.

From #66474 (comment) and #32648 (comment)

Done is:

• Custom 'Justify' format type is removed from dotcom.
• Any support documentation is updated as necessary.

[sejas]

I unassigned me from WordPress/gutenberg#48202 , #66474 and from this issue.

These issues belong to a PT we didn't start pesfPa-rl-p2