Fix: Resolve build errors and logic for agent ippool lease sync

This commit addresses multiple build errors in the agent's local ippool
controller (`pkg/agent/ippool/controller.go`) and refines its lease
synchronization logic:

- Corrected `LeaseTime` type handling when calling `dhcpAllocator.AddLease`,
  passing `specConf.LeaseTime` directly as it's assumed to be `*int`
  based on compiler errors.
- Added missing `sync` and `util` package imports.
- Removed unused variables.
- Corrected the logic for checking lease existence before deletion.
- Deleted the conflicting `pkg/agent/ippool/ippool.go` file that caused
  a method redeclaration error.

These changes are intended to fix the build and ensure the agent's DHCP
lease cache is correctly populated from the IPPool status, particularly
after failovers or restarts.

Author: google-labs-jules[bot]

pkg/agent/ippool/controller.go

@@ -184,7 +184,9 @@ func (c *Controller) Update(ipPool *networkv1.IPPool) error {
 				}
 			}
 
-			leaseTime := int(specConf.LeaseTime)
+			// specConf.LeaseTime is *int (based on compiler error)
+			// dhcpAllocator.AddLease expects *int for leaseTime argument.
+			// Pass specConf.LeaseTime directly.
 			err := c.dhcpAllocator.AddLease(
 				hwAddr,
 				specConf.ServerIP,
@@ -195,7 +197,7 @@ func (c *Controller) Update(ipPool *networkv1.IPPool) error {
 				domainName,   // Nil or from a global config
 				domainSearch, // Empty or from a global config
 				ntpServers,   // Empty or from a global config
-				&leaseTime,
+				specConf.LeaseTime,
 			)
 			if err != nil {
 				logrus.Errorf("Failed to add/update lease for MAC %s, IP %s: %v", hwAddr, clientIPStr, err)