Remove Heap code

DemocracyLab used to use Heap for analytics, but no longer - so all Heap-related code should be removed.

- remove all instances/uses of of [HEAP_ANALYTICS_ID](https://github.com/search?q=repo%3ADemocracyLab%2FCivicTechExchange+HEAP_ANALYTICS_ID&type=code)
- remove heapApi.js from 'common/components/utils'

We are likely to refactor our `metrics` utility for GA4, so please do not delete or remove the metrics.js / associated logging functions.

Then, smoke test the site to make sure render isn't blocked by the removal of heap.

Note for code reviewer: After this code is deployed,
- remove the HEAP_ANALYTICS_ID key on all environments
- remove Heap-related CSP entries. #738 for reference.

Search the repository for HEAP_ANALYTICS_ID, remove the referenced Heap uses, and delete common/components/utils/heapApi.js. Keep metrics.js and its associated logging functions, then smoke test the site to confirm rendering is not blocked. After deployment, the reviewer should remove the HEAP_ANALYTICS_ID environment key and Heap-related CSP entries.

Written by the indexing model from the issue text.