Remove empty lines and rulesets from bundled theme stylesheets

[sabernhardt]

• Removes empty CSS rulesets in Twenty Ten, Twenty Eleven, Twenty Twelve and Twenty Fourteen.
• Removes empty lines within rulesets in Twenty Seventeen and Twenty Twenty-One.
• Rearranges some comments in the SCSS files for Twenty Nineteen so they do not create rulesets without properties.
• Switches some of Twenty Twenty-One's comments from multi-line /* */ format to single-line // format, and those do not appear in the compiled stylesheet.

Props: ravipatel, viralsampat

Trac 59493

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Props sabernhardt, poena.

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[carolinan]

Maybe this comment could just be removed, it seems miss placed since the next code block is not for the galleries in the classic editor.

[sabernhardt]

Removing the comment entirely could be good since it's still under the Classic Editor section.

WordPress/twentynineteen@0064cd5 added the styles, copying the comment from the next ruleset (which was removed before version 1.0). If it is worth having a comment for the blockquote styles, the new explanation could come from the commit message: "Adjust blockquote styles within the classic editor block"

[sabernhardt]

I removed it.

[sabernhardt]

Committed in r58290