Remove "On This Day" dashboard widget from 7.1

[annezazu]

After landing initially https://core.trac.wordpress.org/ticket/65116#ticket, I caught up with Matt and he asked that it be punted from the release. This is partially due to inconsistencies like https://core.trac.wordpress.org/ticket/65783# and the lackluster empty state view as discussed here: ​https://github.com/WordPress/wordpress-develop/pull/12575

It was agreed it's better to not ship something sometimes than to ship something that doesn't move the project forward.

Reverts the On This Day widget from 7.1 as it has been bumped to 7.2

Trac ticket: https://core.trac.wordpress.org/ticket/65801

This reverts:

• ​https://github.com/WordPress/wordpress-develop/commit/6693ea1fec9db0f9324262db344d6267abb6e22b / r62977
• ​https://github.com/WordPress/wordpress-develop/commit/d1c6be6bdae3fb1ef62321df1a8f36060ab26069 / r62968
• ​https://github.com/WordPress/wordpress-develop/commit/ca28cbbad9bc6b4a585c89b32f02162f916fa1bb / r62852
• ​https://github.com/WordPress/wordpress-develop/commit/e8f519d3e69cb4e3e0b3afe024e584fdb452db69 / r62681

## Use of AI Tools

Nope.

[peterwilsoncc]

I've created a ​PR to test the revert but it can be reverted cleanly with these SVN commands:

svn merge -c -62977 .
svn merge -c -62968 .
svn merge -c -62852 .
svn merge -c -62681 .

I'll do this provided the PR's tests complete successfully.

[peterwilsoncc]

In 63001:

Widgets: Revert On This Day dashboard widget.

The On This Day dashboard widget has been bumped from the WordPress 7.1 release to the 7.2 release pending design and behavioural improvements.

This reverts r62977, r62968, r62852, r62681.

Props annezazu, matt, peterwilsoncc.
Fixes #65801.