Revert "Add a notion of "physical" sysroot, use for remote writing"

This reverts commit 1eff3e8343. There
are a few issues with it.  It's not a critical thing for now, so
let's ugly up the git history and revisit when we have time to
debug it and add more tests.

Besides the below issue, I noticed that the simple `ostree remote add`
now writes to `/ostree/repo/config` because we *aren't* using the
`--sysroot` argument.

Closes: https://github.com/ostreedev/ostree/issues/901

Closes: #902
Approved by: mike-nguyen

src/libostree/ostree-sysroot-private.h

@@ -48,8 +48,7 @@ struct OstreeSysroot {
   GLnxLockFile lock;
 
   gboolean loaded;
-
-  gboolean is_physical; /* TRUE if we're pointed at physical storage root and not a deployment */
+  
   GPtrArray *deployments;
   int bootversion;
   int subbootversion;