Bug#247243: don't call update-alternatives --remove on upgrades

["Nikita V. Youshchenko" <yoush@cs.msu.su>]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

I believe this really annoying behaviour may be fixed by not calling 
update-alternatives --remove in prerm if "$1" is "upgrade". This is how 
other packages do.
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.2.4 (GNU/Linux)

iD8DBQFBNavPsTbPknTfAB4RAoU5AJ0f5bm3X5eVgBNfRgYaIJFGougsrwCfZz6T
K4faWs7K1NitH/Ic4eHfizM=
=KEF1
-----END PGP SIGNATURE-----