Log and continue when trying to destroy edges with no edge definition

Summary: Fixes T11201.

Test Plan:
Created bogus edges like this:

INSERT INTO edge (src, type, dst, dateCreated, seq) values ('PHID-TASK-vnddativbialb5p6ymis', 999999, 'quack', UNIX_TIMESTAMP(), 1);

Then ran bin/remove destroy on the relevant object.

Before the patch, destruction halted after hittin the bad edge.

After the patch, a warning is emitted but destruction continues.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T11201

Differential Revision: https://secure.phabricator.com/D16171