fix: disable the Webpack plugins which require the files from the file system

[DimitarTachev]

(Karma is compiling only in memory)

PR Checklist

• The PR title follows our guidelines: https://github.com/NativeScript/NativeScript/blob/master/CONTRIBUTING.md#commit-messages.
• There is an issue for the bug/feature this PR is for. To avoid wasting your time, it's best to open a suggestion issue first and wait for approval before working on it.
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• All existing tests are passing: https://github.com/NativeScript/nativescript-cli/blob/master/CONTRIBUTING.md#contribute-to-the-code-base
• Tests for the changes are included.

What is the current behavior?

The unit testing command with bundle is failing when the GenerateNativeScriptEntryPointsPlugin plugin is used.

What is the new behavior?

The Webpack plugins which require the files from the file system are removed when compiling in Karma.