Clean up codebase.

[MohitMaliFtechiz]

Describe the bug
Since we have fully migrated to compose, there are some methods, extensions classes, etc there which are unused now. We should remove them from our codebase.

Environment

• Version of Kiwix Android : 4.0.0

[kelson42]

I guess there is a tool able to automatically remove all the code which is not used?

[MohitMaliFtechiz]

Yes, in android studio there is tool(Code cleanup, analyze code) which removes the unsused code, but not the whole classes(deleting them). I have deeply cleaned the codebase in #4491 with the help of these tools.