emerge-webrsync: drop lzma support

The lzma snapshots have been replaced by xz snapshots, as discussed in
the "RFC: Remove .lzma in favor of .xz portage snapshots" thread on the
gentoo-dev ml:

http://archives.gentoo.org/gentoo-dev/msg_7de1b57ce531fdf33d33b5b070006436.xml
1 file changed