R: fix port fetch for a few packages which used macports_distfiles

[barracuda156]

Description

Something got broken with macports_distfiles: https://trac.macports.org/ticket/68293
Switch all ports using it to GitHub commits. (The issue initially arose due to r-universe odd manner of stealth-updating.)

Type(s)

• bugfix
• enhancement
• security fix

Tested on

macOS 10.6.8 Server
Xcode 3.2.6

Verification

Have you

• followed our Commit Message Guidelines?
• squashed and minimized your commits?
• checked that there aren't other open pull requests for the same change?
• referenced existing tickets on Trac with full URL?
• checked your Portfile with port lint --nitpick?
• tried existing tests with sudo port test?
• tried a full install with sudo port -vst install?
• tested basic functionality of all binary files?
• checked that the Portfile's most important variants haven't been broken?

[barracuda156]

@herbygillot @reneeotten Sorry to ping again for R stuff, but this is an important fix.

[barracuda156]

@herbygillot Thanks for merging!