⚰️ Remove pluralized from assets

[josemigallas]

It was introduced here:
https://github.com/3scale/system/commit/bd9e3cc1774b94900c465f51b9e9b92b8ae3da0a#diff-1cea3d911776c705a738fa65ff5562262412199642465f153c3cc496429dad19

And then moved to package.json here:
https://github.com/3scale/porta/pull/57/files#diff-7ae45ad102eab3b6d7e7896acd08c427a9b25b346470d7bc6507b6481575d519

And I don't see it's used anywhere (Stats imports if from node_modules).

[mayorova]

Looks like the only usage of the npm-imported pluralize lib is here:

porta/app/javascript/src/Stats/lib/menu.js

Line 82 in 157ca53

{`${period.number} ${pluralize.plural(period.unit)}`}

Given that the period units is always one of: hour, day, month, maybe we can simplify this by just doing ${period.number} ${period.unit}s}` and getting rid of the library 😬