Attach the clearSelect method to mapbox only if it exists

[nickmelnikov82]

Fixes dash issue plotly/dash#2280

Features, Bug fixes, and others:

Before opening a pull request, developer should:

1. make sure they are not on the master branch of their fork as using master for a pull request would make it difficult to fetch upstream changes.
2. fetch latest changes from upstream/master into your fork i.e. origin/master then pull origin/master from you local master.
3. then git rebase master their local dev branch off the latest master which should be sync with upstream/master at this time.
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7. select the Allow edits from maintainers option (see this article for more details).

After opening a pull request, developer:

• should create a new small markdown log file using the PR number e.g. 1010_fix.md or 1010_add.md inside draftlogs folder as described in this README, commit it and push.
• should not force push (i.e. git push -f) to remote branches associated with opened pull requests. Force pushes make it hard for maintainers to keep track of updates. Therefore, if required, please fetch upstream/master and "merge" with master instead of "rebase".

[archmoj]

Thanks very much for the PR.
The bug is addressed in #6367.
Closing.