[TASK] Use autoload map instead of aliases in sysext form

Using the alias map is misleading as it is only used
to force the class loader to cache class names with
lowercased identifier to be able to load the class
with "wrong" casing.

Use the autoload map for that instead and clarify
in that file that it must not be removed for now.

Resolves: #
Releases: master
Change-Id: I8f683ff1d68480a3530a8d2fea62208e66ca947d