Old Eclipse Downloads need broken links cleaned up

Related to #117 (closed) and https://gitlab.eclipse.org/eclipse-wg/ide-wg/eclipseide.org/-/issues/10

There are a bunch of dead links under https://www.eclipse.org/downloads/packages/release

• All the milestone and release candidate pages for old releases should not exist. e.g. https://www.eclipse.org/downloads/packages/release/2021-06 should only have R under it as the https://www.eclipse.org/downloads/packages/release/2021-06/m1 page links to no longer kept downloads

• Some archived releases (ones on archive.eclipse.org) have broken mirror links. e.g. https://www.eclipse.org/downloads/packages/release/galileo/sr1 has https://www.eclipse.org/downloads/download.php?file=/home/data2/httpd/archive.eclipse.org/eclipse/downloads/drops/R-3.5.1-200909170800/eclipse-SDK-3.5.1-linux-gtk-x86_64.tar.gz which is invalid. Notice the extra "/home/data2/httpd/archive.eclipse.org" in the file= part.