Revert "Metadata update for all dev packages"

This reverts commit 069a895d8f6d8d212e75798a275003df3e93506f.
Turns out this didn't really work, and there is no good way to make it work in
a satisfactory way with the current architecture.
Ref: #1316
Fix dev-package update bug

the "url" file could get deleted in some cases.
Merge pull request #1333 from OCamlPro/fix-pin-url

Fixes to dev and pinned package handling