fix: revert avoid css leaking into emitted javascript (#3402)

[dominikg]

…fix for #3610 and partial fix for #2282

This reverts commit 65d333d

Description

The PR #3402 changed the content of css modules to empty string which causes failures for sveltekit testsuite: sveltejs/kit#1622 and also other issues, see #3610 and #2282

Additional context

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What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

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[Dreamacro]

#2144 fixed on 2.3.5. After reverting this commit, it compiled CSS twice.

[dominikg]

Thank you for pointing that out. The revert happened because the change had caused multiple regressions. A proper fix needs to take this into account.

The original PR #3402 intention was to remove an unreferenced variable from js build output. Maybe we should try to find out why this wasn't removed during treeshaking/minification.

Another option would be to check if the regressions were all happening on serve and only remove the css export on build