EGL: Fix a bug in ImageTest During cleanup, we were incorrectly calling glDeleteRenderbuffers on a texture object. Also update comments to correctly reflect intent. Bug: angleproject:5018 Change-Id: I28eaf6a23056f3b09eebb7331620e6a27cb14302 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2406614 Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Mohan Maiya <m.maiya@samsung.com>