bug 892122: Remove dead master instances from bm51/bm53.

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extra : transplant_source : %21H%0B%84U4%DF%40%1A%88%E5%8F%BA-%0B%05%A9%12%0A%E9
bug 892122: speed up reconfigs on linux test masters - migrate 2 more masters to linux64-only instances.
Merge from default

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branch : production