Cleanup babel config

[fregante]

• Drops unused dependencies
• Cleans babel config of unused transforms
• Renames config file to new name (old one is sometimes ignored)

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 98.77%. Comparing base (572e67a) to head (73a2c1d). Report is 1 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #5414 +/- ## ======================================= Coverage 98.77% 98.77% ======================================= Files 51 51 Lines 2855 2855 Branches 867 867 ======================================= Hits 2820 2820 Misses 35 35 ```

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[willdurand]

This looks reasonable to me, @rpl any thoughts?