Remove support for multiple modules with the same soy namespace.
Remove support for multiple modules with the same soy namespace.

This came up when doing some performance analysis and it's too prohibitively expensive to maintain support for.
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=101536474

Medium/closure-templates,atul-bhouraskar/closure-templates,nathancomstock/closure-templates,google/closure-templates,rgpower/closure-templates,iacdingping/closure-templates,iacdingping/closure-templates,Medium/closure-templates,Medium/closure-templates,yext/closure-templates,Medium/closure-templates,rpatil26/closure-templates,google/closure-templates,SerkanSipahi/closure-templates,nathancomstock/closure-templates,yext/closure-templates,yext/closure-templates,rpatil26/closure-templates,atul-bhouraskar/closure-templates,iacdingping/closure-templates,yext/closure-templates,google/closure-templates,rgpower/closure-templates,nathancomstock/closure-templates,rgpower/closure-templates,SerkanSipahi/closure-templates,iacdingping/closure-templates,SerkanSipahi/closure-templates,SerkanSipahi/closure-templates,rpatil26/closure-templates,Medium/closure-templates,atul-bhouraskar/closure-templates,nathancomstock/closure-templates,google/closure-templates,atul-bhouraskar/closure-templates,rgpower/closure-templates,google/closure-templates,rpatil26/closure-templates