docs: Remove switching to preact page

[rschristian]

Builds upon #1350, merge that in first Done

As the title suggests, this removes the 'Switching to Preact' page.

It doesn't really have any purpose at the moment, only directs users to 'Getting Started' for aliasing instructions and also documents some compat APIs, information which are now covered by 'API Reference'. I don't think it has anything to offer and, as such, should be removed.

[github-actions]

Size Change: -160 B (-0.04%)

Total Size: 449 kB

Filename	Size	Change
build/assets/index-********.js	33 kB	-164 B (-0.49%)

ℹ️ View Unchanged

Filename	Size	Change
build/assets/blog-page-********.js	257 B	+3 B (+1.18%)
build/assets/docsearch-********.js	28.9 kB	0 B
build/assets/errors-********.js	342 B	0 B
build/assets/index-********.css	9.85 kB	0 B
build/assets/repl-********.css	1.51 kB	0 B
build/assets/repl-********.js	148 kB	0 B
build/assets/repl-page-********.js	7.66 kB	+1 B (+0.01%)
build/assets/repl.worker-********.js	213 kB	0 B
build/assets/style-********.css	3.07 kB	0 B
build/assets/style.module-********.js	159 B	0 B
build/assets/tutorial-page-********.js	1.99 kB	0 B
build/assets/tutorial-page-********.css	1.76 kB	0 B

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