fix(compiler-sfc): avoid gen useCssVars when targeting SSR

[edison1105]

fix #6926
the repl also has a bug see vuejs/repl#85

[github-actions]

Size Report

Bundles

File	Size	Gzip	Brotli
runtime-dom.global.prod.js	85.9 kB	32.7 kB	29.5 kB
vue.global.prod.js	132 kB	49.4 kB	44.3 kB

Usages

Name	Size	Gzip	Brotli
createApp	47.9 kB	18.9 kB	17.2 kB
createSSRApp	50.7 kB	20 kB	18.2 kB
defineCustomElement	50.3 kB	19.7 kB	18 kB
overall	61.3 kB	23.7 kB	21.6 kB

[yyx990803]

Some context: the reproduction in #6926 was deleted, but the cause of the original issue is that useCssVars codegen was only skipped for SSR + inline mode. So the code is still generated for non-inlined mode (only in webpack / vue-loader SSR setup), and the effect getter is run immediately in SSR, leading to the error.