Delete deprecated `sapi::Sandbox::IsActive` and its remaining call sites.
Delete deprecated `sapi::Sandbox::IsActive` and its remaining call sites.

PiperOrigin-RevId: 390412024
Change-Id: Iab3853b3c40dd4e9b0ff31532e8c41c2583ebc4e

google/sandboxed-api,google/sandboxed-api,google/sandboxed-api,google/sandboxed-api