Stop sending expired testers to an empty page

Both the README and the dialog an expired build puts up pointed at the
Gitea releases page for the next build. That page is empty now - releases
come through another channel - so in a fortnight's time the one message a
tester is guaranteed to read would have sent them somewhere with nothing
on it.

No address in its place: whoever handed them the build is who to ask, and
a URL that goes stale again is worse than no URL. The Source: line stays,
because the repository it names is still there.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

RP_L4/RPL4.CPP

@@ -229,8 +229,7 @@ int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine
                "  Expired  %s\n\n"
                "Test builds are good for a fortnight so that nobody spends an "
                "afternoon chasing something that was fixed a week ago.\n\n"
-               "Grab the current one:\n"
-               "https://gitea.mysticmachines.com/VWE/RP412/releases",
+               "Ask for the current one.",
                RP412_VERSION_LONG, RP412_EXPIRY_TEXT);
             MessageBoxA(NULL, notice, "Red Planet - test build expired",
                MB_OK | MB_ICONWARNING | MB_SETFOREGROUND);

pack-dist.ps1

@@ -299,9 +299,7 @@ documented current one.
 THIS IS A TEST BUILD AND IT GOES STALE. Two weeks after it was built it
 will tell you so and refuse to start, rather than let you spend an
 afternoon on something that was fixed the week before. When that happens,
-grab the current build:
-
-  https://gitea.mysticmachines.com/VWE/RP412/releases
+ask for the current build.
 
 Unzip it over this folder - your environ.ini, bindings.txt, pilot.cfg and
 mfd_layout.cfg all survive.