Maybe remove polymorphic getters #42
Description
I.e. make it so that org-mem-file-title-strict and many others can only be passed a file name, not also an entry interpreted to be inside the file concerned.
That design was mainly because of the existence of org-roam-node-file-title, which takes an org-roam-node object, their equivalent to an org-mem-entry object. However, we don't need to follow in their followsteps. Better simplify the code.