remove IndexedDB keys that shouldn't be keys, and remove unused table, and add commentary

src/db/tables/contacts.ts

@@ -7,5 +7,5 @@ export interface Contact {
 }
 
 export const ContactSchema = {
-  contacts: "&did, name, publicKeyBase64, registered, seesMe",
+  contacts: "&did, name", // no need to key by publicKeyBase64, registered, seesMe
 };

src/db/tables/logs.ts

@@ -6,5 +6,5 @@ export const LogSchema = {
   // Currently keyed by "date" because A) today's log data is what we need so we append, and
   // B) we don't want it to grow so we remove everything if this is the first entry today.
   // See safari-notifications.js logMessage for the associated logic.
-  logs: "date, message",
+  logs: "date", // definitely don't key by the potentially large message field
 };