Don't delete the instance database file on reset

Deleting the file is unsafe as it could be being written to in a
different process and cause the write to end up in an unlinked file. For
example: `cvd reset` could be called concurrently with a `cvd create`
invocation. If the reset command deletes the database file while
`create` is writing to it, the writes will be lost, but `create` will
not find out and continue to start the device, leaving untracked running
devices behind.

`cvd reset` clears the database which effectively truncates the file to
zero size, so it has almost the same effect as deleting it.

Author: jemoreira

base/cvd/cuttlefish/host/commands/cvd/instances/instance_manager.cpp

@@ -296,22 +296,12 @@ Result<void> InstanceManager::Clear() {
 
 Result<void> InstanceManager::Reset() {
   CF_EXPECT(Clear());
-  auto instance_db_deleted = RemoveFile(InstanceDatabasePath());
-  if (!instance_db_deleted) {
-    LOG(ERROR) << "Error deleting instance database file";
-  }
-
   CF_EXPECT(KillAllCuttlefishInstances(false));
   return {};
 }
 
 Result<void> InstanceManager::ResetAndClearInstanceDirs() {
   CF_EXPECT(Clear());
-  auto instance_db_deleted = RemoveFile(InstanceDatabasePath());
-  if (!instance_db_deleted) {
-    LOG(ERROR) << "Error deleting instance database file";
-  }
-
   CF_EXPECT(KillAllCuttlefishInstances(true));
   return {};
 }