Target "Windows-10" instead of the specific build number.

Remove the entries for the Win8 bots which no longer exist.

BUG=669703
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel;master.tryserver.chromium.android:android_optional_gpu_tests_rel
TBR=zmo@chromium.org
NOTRY=true

Review-Url: https://codereview.chromium.org/2594533002
Cr-Commit-Position: refs/heads/master@{#439881}

content/test/gpu/generate_buildbot_json.py

@@ -160,33 +160,11 @@ FYI_WATERFALL = {
       'swarming': True,
       'os_type': 'win',
     },
-    'Win8 Release (NVIDIA)': {
-      'swarming_dimensions': [
-        {
-          'gpu': '10de:104a',
-          'os': 'Windows-10-10586'
-        },
-      ],
-      'build_config': 'Release',
-      'swarming': True,
-      'os_type': 'win',
-    },
-    'Win8 Debug (NVIDIA)': {
-      'swarming_dimensions': [
-        {
-          'gpu': '10de:104a',
-          'os': 'Windows-10-10586'
-        },
-      ],
-      'build_config': 'Debug',
-      'swarming': True,
-      'os_type': 'win',
-    },
     'Win10 Release (NVIDIA)': {
       'swarming_dimensions': [
         {
           'gpu': '10de:104a',
-          'os': 'Windows-10-10586'
+          'os': 'Windows-10'
         },
       ],
       'build_config': 'Release',
@@ -197,7 +175,7 @@ FYI_WATERFALL = {
       'swarming_dimensions': [
         {
           'gpu': '10de:104a',
-          'os': 'Windows-10-10586'
+          'os': 'Windows-10'
         },
       ],
       'build_config': 'Debug',
@@ -269,7 +247,7 @@ FYI_WATERFALL = {
       'swarming_dimensions': [
         {
           'gpu': '8086:0412',
-          'os': 'Windows-10-10586',
+          'os': 'Windows-10',
         },
       ],
       'build_config': 'Release',
@@ -295,7 +273,7 @@ FYI_WATERFALL = {
       'swarming_dimensions': [
         {
           'gpu': '8086:0412',
-          'os': 'Windows-10-10586',
+          'os': 'Windows-10',
         },
       ],
       'build_config': 'Debug',