packages-to-build: fix possible unbreakable cycle in dependency graph

[yoniyes]

bilt assumes that cycles represented as ['A', 'B', 'C'] are the simple case of A-->B-->C-->A (cyclic) and tried to break the cycle by always removing the edge between A and C. However, ['A', 'B', 'C'] can also be the case for A-->B-->C-->B-->A, and in this case, the edge between C and A doesn’t exist. This enables the following loop:

while cycles exist in the dependency graph:
    for each cycle in dependency graph:
        choose edge to remove from each cycle
        remove that edge

In short, the cycle found was assumed to represent a false connectivity between the edges, causing the cycle to never be broken.

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