Remove slow (outdated) speeds from mirror options

[Bryan Quigley]

Given tests results that follow I propose getting rid of all the Kbps options and have the slowest speed to be 1 Mbps.

Local tests would have been better, but all tests were conducted from NJ, USA.

128 Kbps, currently used by (is this a hack to do something unrelated to speed?):
Ge.archive.ubuntu.com-archive - Remote test shows 6.75 MB/s
De.archive.ubuntu.com-archive - Remote test shows 21.6 MB/s
De2.archive.ubuntu.com-archive - Remote test shows 21.6 MB/s
Nz.archive.ubuntu.com-archive - Remote test shows 21.6 MB/s

256 Kbps and 512 Kbps options as their no mirrors currently.

For reference ONLY (not proposing to remove these)
1 Mbps only has:
Botswana / RETENTION RANGE (PTY) LTD in - http://mirror.retentionrange.co.bw/ubuntu/. Remote tests, indicate this could be very limited.

2 Mbps only has:
Kuwait / Gulf University for Science & Technology - http://repo.gust.edu.kw/ubuntu/ Remote tests this is somewhere around 4 Mbps/
India / Pramati Technologies - http://mirror.pramati.com/ubuntu/ Remote tests, indicate this could be very limited.

[Bryan Quigley (bryanquigley)]

@LaMont
Any chance you could bump those mirrors to 1 Mbps so I can propose this change? Thanks!