Remove branchName from unmaintained branch

Since doctrine/doctrine-website#372, they are no
longer necessary, it's possible to rely on tags. Once this is merged,
the branches can be removed.

Author: greg0ire

.doctrine-project.json

@@ -25,31 +25,26 @@
         },
         {
             "name": "3.4",
-            "branchName": "3.4.x",
             "slug": "3.4",
             "maintained": false
         },
         {
             "name": "3.3",
-            "branchName": "3.3.x",
             "slug": "3.3",
             "maintained": false
         },
         {
             "name": "3.2",
-            "branchName": "3.2.x",
             "slug": "3.2",
             "maintained": false
         },
         {
             "name": "3.1",
-            "branchName": "3.1.x",
             "slug": "3.1",
             "maintained": false
         },
         {
             "name": "3.0",
-            "branchName": "3.0.x",
             "slug": "3.0",
             "maintained": false
         },
@@ -67,61 +62,51 @@
         },
         {
             "name": "2.19",
-            "branchName": "2.19.x",
             "slug": "2.19",
             "maintained": false
         },
         {
             "name": "2.18",
-            "branchName": "2.18.x",
             "slug": "2.18",
             "maintained": false
         },
         {
             "name": "2.17",
-            "branchName": "2.17.x",
             "slug": "2.17",
             "maintained": false
         },
         {
             "name": "2.16",
-            "branchName": "2.16.x",
             "slug": "2.16",
             "maintained": false
         },
         {
             "name": "2.15",
-            "branchName": "2.15.x",
             "slug": "2.15",
             "maintained": false
         },
         {
             "name": "2.14",
-            "branchName": "2.14.x",
             "slug": "2.14",
             "maintained": false
         },
         {
             "name": "2.13",
-            "branchName": "2.13.x",
             "slug": "2.13",
             "maintained": false
         },
         {
             "name": "2.12",
-            "branchName": "2.12.x",
             "slug": "2.12",
             "maintained": false
         },
         {
             "name": "2.11",
-            "branchName": "2.11.x",
             "slug": "2.11",
             "maintained": false
         },
         {
             "name": "2.10",
-            "branchName": "2.10.x",
             "slug": "2.10",
             "maintained": false
         }