Simplify webpack-fluid-loader's webpack config

[CraigMacomber]

Description

Simplify webpack-fluid-loader's webpack config. This modernizes it based off of the content in examples/utils/webpack-fluid-loader/src/defaultWebpackConfig.ts. No longer needed workarounds have been removed.

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Its unclear to me what this config is used for: It's hard coded into "development" and the package is in @fluid-example so I suspect its either just for testing, or just used by examples. Given that the bundle is generated into "dist", it seems like its only available in one of the two build configurations, which also makes me things its not actually used for anything other that testing if it can webpack without errors.