Remove unused (#2501)

* Remove Moxa

- [Undetected](https://www.wappalyzer.com/technologies/moxa)
- [Website](https://www.moxa.com/) says "Industrial IOT", unlikely to be
  detected/useful

* Remove Sparql

- [undetected](https://www.wappalyzer.com/technologies/sparql)
- no way to be detected, must have been a dependency at some point in the past

* Remove ARC Forum

- [Undetected](https://www.wappalyzer.com/technologies/arc-forum)
- The [website](AAA) says: "This site is about Arc, a new dialect of Lisp.",
  and also "Arc is unfinished. It's missing things you'd need to solve some types of problems. But it works well for basic web apps.".
  I dont think that anyone is using it in production

* Remove C++, since it can't be detected

* Remove Gazelle

- What.cd is dead
- The project isn't maintained anymore

src/apps.json

@@ -805,14 +805,6 @@
       "script": "arastta\\.js",
       "website": "http://arastta.org"
     },
-    "Arc Forum": {
-      "cats": [
-        2
-      ],
-      "html": "ping\\.src = node\\.href;\\s+[^>]+\\s+}\\s+</script>",
-      "icon": "Arc Forum.png",
-      "website": "http://arclanguage.org"
-    },
     "ArcGIS API for JavaScript": {
       "cats": [
         35
@@ -1435,13 +1427,6 @@
       "script": "^https?://s\\d\\.buysellads\\.com/",
       "website": "http://buysellads.com"
     },
-    "C++": {
-      "cats": [
-        27
-      ],
-      "icon": "C++.png",
-      "website": "http://isocpp.org"
-    },
     "CDN77": {
       "cats": [
         31
@@ -3441,20 +3426,7 @@
       },
       "website": "https://get.gaug.es"
     },
-    "Gazelle": {
-      "cats": [
-        29
-      ],
-      "html": [
-        "<!-- Extra divs, for stylesheet developers to add imagery -->",
-        "<link rel=\"alternate\" type=\"application/rss+xml\" href=\"[^\"]+\" title=\"[^\"]+ - Gazelle Change Log\""
-      ],
-      "js": {
-        "GazURL": ""
-      },
-      "website": "https://whatcd.github.io/Gazelle/"
-    },
-    "Gentoo": {
+		"Gentoo": {
       "cats": [
         28
       ],
@@ -6487,16 +6459,6 @@
       },
       "website": "http://movabletype.org"
     },
-    "Moxa": {
-      "cats": [
-        37
-      ],
-      "headers": {
-        "Server": "MoxaHttp(?:/([\\d.]+))?\\;version:\\1"
-      },
-      "icon": "Moxa.png",
-      "website": "http://moxa.com"
-    },
     "Mozard Suite": {
       "cats": [
         1
@@ -9220,12 +9182,6 @@
       },
       "website": "http://www.schillmania.com/projects/soundmanager2"
     },
-    "Sparql": {
-      "cats": [
-        27
-      ],
-      "website": "https://www.w3.org/TR/sparql11-overview/"
-    },
     "Sphinx": {
       "cats": [
         4