I am new to Emacs Lisp and the feeling is like it lacks strictness (and namespaces, and more...).
To be more comfortable with it I need a
way to make interpreter/byte compiler complain a lot if I use deprecated or obsolete function or variable (even better - hide them). Why this is not looks so simple and removing corresponding .el packages will not work is obvious - they may be needed by some legacy code.
Also, if it is possible, turning off all aliases would be nice. In my opinion they are there only for backwards compatibility, which I do not need. Because of setting this one globally can ruin something, I hope there is something like use strict in JavaScript, which can be applied to the inner body, so the effect is neatly localized.
Do not get me wrong, I think that global namespace of the Elisp is like a dump and if it could be any cleaner, why not?
To put in one sentence: how to make Elisp global namespace obsoleteless and deprecateless, as slim as possible?
I don't know of an Emacs Lisp linter that is built in to Emacs.
I do two things for my own code to try to ensure some level of cleanliness.
First, I make sure that byte-compiling the code doesn't give any errors or warnings. The byte compiler does a certain amount of checking.
Second, I enable lexical binding. This lets the byte compiler detect a few more possible warnings.
This is about the best you can do with the built-in tools. If you want to go further you could write your own tree walker to perform whatever other tests you like.