[infra] Remove ABI builder from the test matrix

This is no longer a feature we plan to support.

Change-Id: Ie916f3bbb0313c98863e360472f126c24340013d
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/156026
Reviewed-by: William Hesse <[email protected]>

Author: athomas

tools/bots/test_matrix.json

@@ -913,9 +913,6 @@
         ]
       }
     },
-    "dartkb-abi-linux-release-x64": {
-      "__comment__": "This configuration is only used for a custom test runner. If it conflicts with a new configuration you are adding, you can make this configuration more specific by adding options."
-    },
     "dartdevk-checked-(linux|mac|win)-(debug|product|release)-(chrome|firefox)": {
       "options": {
         "checked": true,
@@ -3441,30 +3438,6 @@
         }
       ]
     },
-    {
-      "builders": [
-        "vm-dartkb-linux-release-x64-abi"
-      ],
-      "meta": {
-        "description": "This configuration runs tests for each supported ABI version."
-      },
-      "steps": [
-        {
-          "name": "build dart",
-          "script": "tools/build.py",
-          "arguments": [
-            "--bytecode",
-            "create_sdk_with_abi_versions"
-          ]
-        },
-        {
-          "name": "run tests",
-          "script": "tools/run_abi_tests.py",
-          "testRunner": true,
-          "arguments": ["-ndartkb-abi-linux-release-x64"]
-        }
-      ]
-    },
     {
       "builders": [
         "vm-kernel-precomp-linux-debug-simarm_x64",