samples: allow only one pair of region tags

[anguillanneuf]

Really odd. #527 actually messed up the README:

[snippet-bot]

Here is the summary of changes.

You are about to delete 1 region tag.

• samples/snippets/pom.xml:90, tag pubsub_install_with_bom

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[generated-files-bot]

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

• samples/snippets/pom.xml

[codecov]

Codecov Report

Merging #532 (0d967d2) into master (325fed0) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master     #532   +/-   ##
=========================================
  Coverage     78.85%   78.85%           
  Complexity      376      376           
=========================================
  Files            27       27           
  Lines          3414     3414           
  Branches        171      171           
=========================================
  Hits           2692     2692           
  Misses          650      650           
  Partials         72       72           

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[chingor13]

This is very odd. Try using the exclude tag syntax instead of 2 duplicate region tags (which is allowed on cloud site, but not parsed in https://github.com/googleapis/synthtool/blob/master/synthtool/gcp/snippets.py)

[chingor13]

I don't think you need the region tag to exclude