[lib] Simplify getRelativeMemberInfos

Summary:
In subsequent diff going to split into two separate functions: `getLegacyRelativeMemberInfos` and `getMinimallyEncodedRelativeMemberInfos` and then toggle between then based on whether input `RawThreadInfo` is `minimallyEncoded` or not.

Since that diff is about duplicating existing functionality and branching... figure changing the actual functionality may be annoying for reviewers even though it's minimal (?)

---

Depends on D10227

Test Plan: CI/`flow`/etc.

Reviewers: ashoat, ginsu, tomek, rohan

Reviewed By: ashoat

Differential Revision: https://phab.comm.dev/D10233

lib/selectors/user-selectors.js

@@ -73,21 +73,15 @@ function getRelativeMemberInfos(
       : null;
     if (memberInfo.id === currentUserID) {
       relativeMemberInfos.unshift({
-        id: memberInfo.id,
-        role: memberInfo.role,
-        permissions: memberInfo.permissions,
+        ...memberInfo,
         username,
         isViewer: true,
-        isSender: memberInfo.isSender,
       });
     } else {
       relativeMemberInfos.push({
-        id: memberInfo.id,
-        role: memberInfo.role,
-        permissions: memberInfo.permissions,
+        ...memberInfo,
         username,
         isViewer: false,
-        isSender: memberInfo.isSender,
       });
     }
   }