1. Removes the access check callback, which was kind of confusing.
1. Requires `CheckedPath` for everything in the `FileSystem` trait to
ensure we're always checking permissions.
This slightly degrades the performance of CJS export analysis on
subsequent runs because I changed it to no longer cache in the DENO_DIR
with this PR (denort now properly has no idea about the DENO_DIR). We'll
have to change it to embed this data in the binary and that will also
allow us to get rid of swc in denort (will do that in a follow-up PR).