remove no longer used branches in McLachlan

[Roland Haas]

mclachlan contains a number of feature branches that have since been merged into master or only served as reference points while merging. This should be removed to reduce the number of top level and merged branches. Namely:

• rewrite https://bitbucket.org/einsteintoolkit/mclachlan/branch/rewrite
• integrate_rewrite https://bitbucket.org/einsteintoolkit/mclachlan/branch/integrate-rewrite
• CCZ4 https://bitbucket.org/einsteintoolkit/mclachlan/branch/CCZ4
• vector: https://bitbucket.org/einsteintoolkit/mclachlan/branch/vector
• admcons_intelbug: https://bitbucket.org/einsteintoolkit/mclachlan/branch/ianhinder/admcons_intelbug

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