While it would be nice to support translated documentation, this is unlikely to
happen in the near future. Cleaning up the /en from the permalinks makes the URLs shorter,
easier to remember, and more consistent with https://www.bitcoinabc.org/doc/dev/ which does
not have translation support (and is unlikely to ever have it, given the development overhead
of maintaining translated comments).
The /en was retained in the file paths since it does not negatively impact the build system
and it gives a hint for where translated RPC documentation could go in the future. When that
day comes, then we can consider how those translated docs fit into our routing scheme.