Removing MSAN unpoison workarounds for clang-9 and below.
Removing MSAN unpoison workarounds for clang-9 and below.

MSAN unpoison workaround was introduced in 13dbdff9b76f (0.3.9) for a
false-positive bug in clang-9 and below.

Also, after 80d95b2881f6 (0.4.1) the bug is not triggered anymore.

nginx/njs,nginx/njs,nginx/njs,nginx/njs,nginx/njs,nginx/njs