Bump external/libbtf from `69e0268` to `2de28d7` #1441

Job	Run time
build_ubuntu (Debug, tests)	26m 57s
build_windows (Debug, tests)	36m 16s
build_windows (Debug, library)	4m 18s
build_ubuntu (Debug, library)	1m 14s
build_windows (Release, tests)	9m 21s
build_windows (Release, library)	5m 31s
build_ubuntu (Release, tests)	5m 53s
build_ubuntu (Release, library)	1m 9s
	1h 30m 39s

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