bug#73681: Maybe partly undo the patch on Elisp comp-el-to-eln-filename

[Martin Edström]

Hi, I suggest to maybe amend one of the things done by this patchset:  
https://issues.guix.gnu.org/67260

It undoes the hashing effect of the Elisp function `comp-el-to-eln-filename`, 
and that seems likely to cause issues downstream, for example in my Emacs 
package: https://github.com/meedstrom/org-node/issues/60.

To summarize: that function is supposed to generate a filename with a hash 
based not only the filename but the contents of the file.  While it makes sense 
in Guix to ignore the contribution of the filename, I believe it should still 
output a new filename when the contents change.

Otherwise there seems to be no way for a downstream package to ensure that it 
is using an up-to-date .eln variant of an .el file.

I may have missed something though.  Can someone in the know tell me what 
happens if you have not updated Emacs (which if I understand correctly, means 
ELN-DIR does not change), but you do update an Elisp package, whether through 
Guix or through Emacs' own package managers. Will Emacs then possibly load an 
old .eln?  

I do not believe that user options like `load-prefer-newer` would affect it. It 
would just rely on running the aforementioned function and counting on it to 
output an .eln filename that does not exist if the source is newer.