Remove CSS3_Syntax package (#6482)

This is an ancient ST2 package of mine that has been deprecated since
2014. It has been replaced by the CSS3 package. I'm deleting the
CSS3_Syntax repo.

repository/c.json

@@ -3732,16 +3732,6 @@
 				}
 			]
 		},
-		{
-			"name": "CSS3_Syntax",
-			"details": "https://github.com/y0ssar1an/CSS3_Syntax",
-			"releases": [
-				{
-					"sublime_text": "<3000",
-					"tags": true
-				}
-			]
-		},
 		{
 			"name": "CSScomb",
 			"details": "https://github.com/csscomb/sublime-csscomb",