Don't run formula simplifier when building server-expanded layers

[chuckdumont]

The boolean formula simplifier is needed when doing require list expansion, but not when doing server-side expansion of dependencies, but it was still getting invoked when the layer builder called ModuleDepInfo.getPluginPrefixes() for the purpose of determining whether to include a module in a server-expanded layer. Because of the poor performance characteristics of the Quinne-Mcluskey algorithm used by the boolean formula simplifier when there are a large number of expressions, it is desirable to avoid the boolean formula simplifier when doing server-side expansion.

[chuckdumont]

@ddumont please review

[hcldan]

LGTM