Do not recommend Google Cache in the documentation

[Gallaecio]

From the feedback at Using Scrapy on a Google cache of a website, I think we should stop recommending Google Cache in the Scrapy documentation.

We should review the terms of use of the Wayback Machine from archive.org, and see if we can recommend that instead.

[yashrajjain726]

If you want, I will do it.

[farsene]

Is this issue still relevant? If so, I'd like to work on it

[Gallaecio]

Removing the current recommendation is still relevant, but instead of the Wayback Machine we should probably recommend:

• https://commoncrawl.org/
• https://datasetsearch.research.google.com/

[farsene]

@Gallaecio thanks for approving my PR, I don't have write access to merge it. Can you do it please?

[Gallaecio]

@Farsene1 We usually go for 2 maintainer approvals before merging. When another maintainer gets a chance to review and approve the change, we will merge it. Please, be patient.