Revert "Add more-horizontal-rectangle icon"

This reverts commit 3960c6ee0c.

icons/more-horizontal-rectangle.json

@@ -1,29 +0,0 @@
-{
-  "$schema": "../icon.schema.json",
-  "contributors": [
-    "danielbayley"
-  ],
-  "tags": [
-    "ellipsis",
-    "et cetera",
-    "etc",
-    "loader",
-    "loading",
-    "progress",
-    "pending",
-    "throbber",
-    "menu",
-    "options",
-    "operator",
-    "code",
-    "spread",
-    "rest",
-    "…",
-    "..."
-  ],
-  "categories": [
-    "layout",
-    "development",
-    "shapes"
-  ]
-}

icons/more-horizontal-rectangle.svg

@@ -1,16 +0,0 @@
-<svg
-  xmlns="http://www.w3.org/2000/svg"
-  width="24"
-  height="24"
-  viewBox="0 0 24 24"
-  fill="none"
-  stroke="currentColor"
-  stroke-width="2"
-  stroke-linecap="round"
-  stroke-linejoin="round"
->
-  <rect width="20" height="12" x="2" y="6" rx="2" />
-  <circle cx="6.5" cy="12" r=".5" />
-  <circle cx="12" cy="12" r=".5" />
-  <circle cx="17.5" cy="12" r=".5" />
-</svg>