Removed deprecated and unused files from lib/Mage

[fballiano]

THIS PR TARGETS V21

These files seem to be unused (unreferenced anywhere).
lib/Mage/Cache/Backend/Redis.php is also deprecated since many years (I've tested redis cache without this file and it works perfectly)

[kiatng]

There may be local.xml with this setting:

<backend>Mage_Cache_Backend_Redis</backend>

That needs to change to this after this PR:

<backend>Cm_Cache_Backend_Redis</backend>

Ref https://github.com/colinmollenhour/Cm_Cache_Backend_Redis.

[fballiano]

I'll make sure to write that in the release notes for v21

[kiatng]

Found this:

magento-lts/lib/Mage/DB/Mysqli.php

Line 77 in 304a23c

throw new Mage_DB_Exception(mysqli_connect_error($this->conn));

oops...it's circular reference in Mage_DB_Mysqli

[fballiano]

exactly, that why I think it's time to clean out those files

[fballiano]

note that the PR targets next