Camera: Fix double-free in removeCamera

When a camera is removed, |hidlMetadata| takes over ownership of
|metadata|. Therefore, we should not free |metadata| again.

Bug: 180014486
Test: Remove an external camera, and no crashes were observed.
Marged-In: I85246067f8753911cbcb58af24a46f12962226f3
Change-Id: I85246067f8753911cbcb58af24a46f12962226f3
(cherry picked from commit f36a439e3a97315a9f0a8661ea77aff61fb79c82)
(cherry picked from commit 682abf40)