Multi_tenant is the new payload_not_root

Trying to have more fine-grained Rust configs than feature flags was
actually a terrible idea, and means extra work if I need to add
something that is multi-tenant related but not root related.

Use consistent naming throughout instead.

Bug: 302677468
Test: Builds
Change-Id: I2dfe97e8c62f24590522df89d9b373774a43d495
diff --git a/encryptedstore/src/main.rs b/encryptedstore/src/main.rs
index db3d4f6..dcb1cba 100644
--- a/encryptedstore/src/main.rs
+++ b/encryptedstore/src/main.rs
@@ -94,7 +94,7 @@
     }
     mount(&crypt_device, mountpoint)
         .with_context(|| format!("Unable to mount {:?}", crypt_device))?;
-    if cfg!(payload_not_root) && needs_formatting {
+    if cfg!(multi_tenant) && needs_formatting {
         set_root_dir_permissions(mountpoint)?;
     }
     Ok(())