[histogram] percentile value in tooltip shows formula instead of value

[kamalkeshavani-aiinside]

A clear and concise description of what the bug is.

How to reproduce the bug

1. Go to 'FCC New Coder Survey 2018' sample dashboard.
2. Check the tooltip in histogram chart 'Age distribution of respondents'

Expected results

In tooltip, percentile value should be shown.

Actual results

In tooltip, percentile value formula is shown.

Screenshots

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Environment

(please complete the following information):

• browser type and version: Chrome 95.0.4638.69
• superset version: master
• python version: 3.7
• node.js version: 14.15.5
• any feature flags active: default

Checklist

Make sure to follow these steps before submitting your issue - thank you!

• I have checked the superset logs for python stacktraces and included it here as text if there are any.
• I have reproduced the issue with at least the latest released version of superset.
• I have checked the issue tracker for the same issue and I haven't found one similar.

Additional context

Add any other context about the problem here.
cc: @villebro