Remove deprecated v1alpha1/ExternalEntity #31949

Job	Run time
Verify docs and spelling	1m 6s
Check whether tests need to be run based on diff	18s
Unit test (ubuntu-latest)	6m 29s
Unit test (windows-2022)	11m 57s
Golangci-lint (ubuntu-latest)	7m 52s
Integration test	10m 17s
Build Antrea and antctl binaries	9m 52s
Go benchmark test	4m 36s
Golangci-lint (macos-latest)	9m 4s
Check tidy, code generation and manifest	5m 41s
Build Antrea Windows binaries	1m 50s
	1h 9m 2s

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