Remove .html files from distfiles mirrors

[ryandesign (Ryan Carsten Schmidt)]

When a port fails to fetch because the upstream server delivered an HTML file instead of the real file, MacPorts helpfully renames the distfile to end with .html and prints a message advising the user to look at this file. But these files are not needed or wanted on the distfiles mirrors and should be removed. Perhaps a nightly task could do this. This directory contains an example of such a file:

​http://distfiles.macports.org/openmpi-devel/

This is a similar request to #18952, which five years later still needs to be implemented. Both requests should be simple to implement with a one-line invocation of the find command.

[ryandesign (Ryan Carsten Schmidt)]

I've done a one-time removal of unwanted .html files from the distfiles server. Once mirroring is set up again (#53347) we should make sure that we don't preserve unwanted .html files (while preserving wanted .html files).