chore: de-duplicating region tag

[meredithslota]

Addressing a region tag conflict with the other nodejs-firestore quickstart sample.

[snippet-bot]

Here is the summary of changes.

You are about to add 1 region tag.

• samples/quickstart.js:15, tag firestore_session_quickstart

You are about to delete 1 region tag.

• samples/quickstart.js:15, tag firestore_quickstart

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[meredithslota]

Note that SnippetBot is referring to this page (https://cloud.google.com/firestore/docs/samples/firestore-quickstart#firestore_quickstart-nodejs) which is actually the incorrect sample to be included there, and the rationale for de-duplicating this region tag. Sample Browser will automatically pick up the correct sample once the region tag is unique.

[generated-files-bot]

Warning: This pull request is touching the following templated files:

• .kokoro/publish.sh - .kokoro files are templated and should be updated in synthtool
• .kokoro/release/publish.cfg - .kokoro files are templated and should be updated in synthtool