Correctly unload variable aliases.

Correctly unload variable aliases.

* src/eval.c (Finternal_delete_indirect_variable): Add function.
* lisp/loadhist.el (loadhist-unload-element): Use it for variable
aliases.
* test/src/eval-tests.el (eval-tests--internal-delete-indirect-variable):
Test function `internal-delete-indirect-variable'.
* test/lisp/loadhist-tests.el (loadhist-test-unload-feature-alias):
* test/lisp/loadhist-resources/loadhist--alias.el: Test unloading of
features that define variable aliases.  (Bug#76748)

(cherry picked from commit 7f2e4508cebe76a885b72ca4789ae839d5bd45e1)