fix: cp-12.15.0 remove sentry cdn url from sentry script (#31360)

We don't use this code path, but just having this url appear in our
extension bundle makes it looks like we could load code from an external
source, something which is not permitted by extension web stores.

To test: download the build (or build it yourself), extract it, search
the source the code for `browser.sentry-cdn.com`. It should not exist.

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Author: davidmurdoch