runtime: remove usage of weak_ptr in attach manager #344

Job	Run time
build-runtime	3m 40s
build-and-test (libbpf-tools/opensnoop, ./opensnoop, ./victim, true, 0 test.txt)	43s
build-and-test (libbpf-tools/statsnoop, ./statsnoop, ./victim, true, victim 0 0 ...	50s
build-and-test (malloc, ./malloc, ./victim, false, malloc calls: )	40s
build-and-test (minimal, ./uprobe, ./victim, false)	42s
build-and-test (opensnoop, ./opensnoop, ./victim, true, 0 test.txt)	51s
build-and-test (sslsniff, ./sslsniff, /bin/wget https://www.google.com, false, ----- DATA -----)	36s
build-and-test (libbpf-tools/bashreadline, ./readline, /bin/bash, false, info)	36s
build-and-test (libbpf-tools/syscount, ./syscount, /bin/bash, false, info)	55s
	9m 33s

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