[infra/tools] Delete scripts in tools/gardening

These scripts were written for dealing with status files and failure
logs in the old testing workflow and seem no longer useful.

Change-Id: Ic01291bdb34a14c12c32b977532eea520782314d
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/147543
Auto-Submit: Karl Klose <[email protected]>
Commit-Queue: Karl Klose <[email protected]>
Reviewed-by: Martin Kustermann <[email protected]>
Reviewed-by: Alexander Thomas <[email protected]>

Author: karlklose

tools/bots/test_matrix.json

@@ -3341,14 +3341,6 @@
             "runtime/observatory"
           ]
         },
-        {
-          "name": "analyze tools/gardening",
-          "script": "out/ReleaseX64/dart-sdk/bin/dartanalyzer",
-          "arguments": [
-            "--fatal-warnings",
-            "tools/gardening"
-          ]
-        },
         {
           "name": "dartanalyzer --batch tests",
           "arguments": [