Use `feature` RPC to populate `AmendmentEnable` tx Simple page.

[pdp2121]

With the new feature RPC introduced in rippled 2.2.0, EnableAmendment tx Simple page can populate its data using amendment id without dependence on xrpl.org and rippled docs (which change pretty frequently):

https://github.com/ripple/explorer/blob/staging/src/containers/shared/amendmentUtils.ts

The logic would be simplified and consistency would be improved