chore: remove accidentally committed guest_agent binary

Updated .gitignore to cover both guest-agent and guest_agent naming
patterns and removed the tracked binary from the repository.

Author: rgarcia

.gitignore

@@ -21,6 +21,7 @@ cloud-hypervisor
 cloud-hypervisor/**
 lib/system/exec_agent/exec-agent
 lib/system/guest_agent/guest-agent
+lib/system/guest_agent/guest_agent
 
 # Envoy binaries
 lib/ingress/binaries/**