docs: remove browsers readme obsolete information

[MikeMcC399]

Issue

browsers/README.md contains outdated information:

• https://chromium.cypress.io/ is no longer active as a source of Chromium versions
• The explanation of tags in browsers/README.md > Naming scheme and in browsers/README.md > Tags is outdated and duplicates information in README > Tag Selection
• The section browsers/README.md > Other images is outdated, unhelpfully links to https://on.cypress.io/docker, and duplicates information in README > Cypress/Factory

Change

Remove the outdated / duplicate information from browsers/README.md.

[cypress-app-bot]

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