Delete chromium valgrind bots.

scripts/slave/gatekeeper.json

 {
   "comment": ["This is a configuration file for gatekeeper_ng.py",
               "Look at that for documentation on this file's format."],
 
   "masters": {
     "https://build.chromium.org/p/chromium": [
       {
         "categories": [
           "chromium_tree_closer"
         ],
@@ skipping 377 matching lines @@
       {
         "categories": [
           "chromium_memory_fyi"
         ],
         "sheriff_classes": ["sheriff_memory"],
 
         "builders": {
           "Chromium Linux MSan Builder": {},
           "Linux MSan Tests": {},
           "Chromium Linux ChromeOS MSan Builder": {},
-          "Linux ChromeOS MSan Tests": {},
-          "Chromium Linux Builder (valgrind)": {},
-          "Linux Tests (valgrind)(1)": {},
-          "Linux Tests (valgrind)(2)": {},
-          "Linux Tests (valgrind)(3)": {},
-          "Linux Tests (valgrind)(4)": {},
-          "Linux Tests (valgrind)(5)": {}
+          "Linux ChromeOS MSan Tests": {}
         }
       }
     ],
     "https://build.chromium.org/p/chromium.perf": [
       {
         "forgive_all": "true",
 
         "subject_template": "%(project_name)s %(builder_name)s %(result)s",
 
         "categories": [
@@ skipping 541 matching lines @@
         "cleanup_temp",
         "taskkill"
       ],
       "closing_optional": [
         "compile",
         "gn"
       ]
     }
   }
 }