a library that depends on jquery was created. After that, a version where all dependant calls were replaced with original jquery code. Most parts of such code were removed as redundant. Should be jquery somehow mentioned in such case?
The MIT license does not require that you in some way reference the original project when you copy some code.
The MIT license does require that you copy the copyright and license text along with the code that you copy. Depending on how the copyright statement is formulated, this can become effectively a reference to the original project.