docs(templates): remove samples/quickstart, post-processor will generate it

[sofisl]

See: https://github.com/googleapis/synthtool/pull/1527

[snippet-bot[bot]]

Here is the summary of changes.

You are about to delete 2 region tags.

• packages/gapic-node-templating/snapshots/templating.test.js:87, tag quickstart
• packages/gapic-node-templating/templates/bootstrap-templates/samples/quickstart.js:19, tag quickstart

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