Drop project--value-in-dir

Drop project--value-in-dir

Drop the project--value-in-dir mechanics, where the user could edit
the value in .dir-locals.el and have it applied instantly without
reverting the current buffer.  It made working in remote buffers with
enable-remote-dir-locals non-nil slower, which doesn't seem worth it
for a minor improvement of an infrequent operation.  Also less
compexity overall.

* lisp/progmodes/project.el (project-try-vc, project-files)
(project--vc-list-files, project-ignores, project-buffers):
Use the user options directly.
(project--vc-merge-submodules-p, project--value-in-dir):
Delete functions.