fix(css): Remove ::first-line from margin* props (#706)

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### Description

Correct the `alsoAppliesTo` for the CSS `margin` and
`margin-{top,bottom,left,right.trim}` properties.

### Motivation

The data claims that `margin*` properties apply to the `::first-line`
pseudoelement, which is untrue. They apply to `::first-letter`, but not
`::first-line`. As reported by @Akindin in mdn/content#31806.

### Additional details

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places providing more context -->

### Related issues and pull requests

Fixes mdn/content#31806

Author: ferdnyc

css/properties.json

@@ -6384,8 +6384,7 @@
     ],
     "order": "uniqueOrder",
     "alsoAppliesTo": [
-      "::first-letter",
-      "::first-line"
+      "::first-letter"
     ],
     "status": "standard",
     "mdn_url": "https://developer.mozilla.org/docs/Web/CSS/margin"
@@ -6458,8 +6457,7 @@
     "computed": "percentageAsSpecifiedOrAbsoluteLength",
     "order": "uniqueOrder",
     "alsoAppliesTo": [
-      "::first-letter",
-      "::first-line"
+      "::first-letter"
     ],
     "status": "standard",
     "mdn_url": "https://developer.mozilla.org/docs/Web/CSS/margin-bottom"
@@ -6532,8 +6530,7 @@
     "computed": "percentageAsSpecifiedOrAbsoluteLength",
     "order": "uniqueOrder",
     "alsoAppliesTo": [
-      "::first-letter",
-      "::first-line"
+      "::first-letter"
     ],
     "status": "standard",
     "mdn_url": "https://developer.mozilla.org/docs/Web/CSS/margin-left"
@@ -6552,8 +6549,7 @@
     "computed": "percentageAsSpecifiedOrAbsoluteLength",
     "order": "uniqueOrder",
     "alsoAppliesTo": [
-      "::first-letter",
-      "::first-line"
+      "::first-letter"
     ],
     "status": "standard",
     "mdn_url": "https://developer.mozilla.org/docs/Web/CSS/margin-right"
@@ -6572,8 +6568,7 @@
     "computed": "percentageAsSpecifiedOrAbsoluteLength",
     "order": "uniqueOrder",
     "alsoAppliesTo": [
-      "::first-letter",
-      "::first-line"
+      "::first-letter"
     ],
     "status": "standard",
     "mdn_url": "https://developer.mozilla.org/docs/Web/CSS/margin-top"
@@ -6592,8 +6587,7 @@
     "computed": "asSpecified",
     "order": "perGrammar",
     "alsoAppliesTo": [
-      "::first-letter",
-      "::first-line"
+      "::first-letter"
     ],
     "status": "experimental",
     "mdn_url": "https://developer.mozilla.org/docs/Web/CSS/margin-trim"