Fix instrumentation tests failing with INSTALL_PARSE_FAILED_INCONSISTENT_CERTIFICATES

When a cached AVD snapshot has LeakCanary packages installed with different
signing certificates than the current build, Android refuses to reinstall them.
Fix by explicitly uninstalling all known LeakCanary packages before running
connectedCheck, so the fresh build APKs always install cleanly.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>