src: remove SecureContext `_external` getter
This is unused inside Node core, so nothing good can come from keeping it around.
(If somebody wants to label this semver-major
, I don’t really care, but it’s really just unused code in an internal API that can’t really be used in a meaningful way.)
Checklist
-
make -j4 test
(UNIX), orvcbuild test
(Windows) passes -
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