Mark good devicelab tests as non-flaky (#13271)

dev/devicelab/manifest.yaml

@@ -40,7 +40,6 @@ tasks:
       Layout sample app for Android from Linux.
     stage: devicelab
     required_agent_capabilities: ["linux/android"]
-    flaky: true
 
   complex_layout_ios__compile:
     description: >
@@ -48,7 +47,6 @@ tasks:
       Layout sample app for iOS from Mac.
     stage: devicelab_ios
     required_agent_capabilities: ["has-ios-device"]
-    flaky: true
 
   complex_layout_win__compile:
     description: >
@@ -56,7 +54,6 @@ tasks:
       Layout for Android from Windows.
     stage: devicelab_win
     required_agent_capabilities: ["windows"]
-    flaky: true
 
   basic_material_app_android__compile:
     description: >
@@ -64,7 +61,6 @@ tasks:
       app for Android from Linux.
     stage: devicelab
     required_agent_capabilities: ["linux/android"]
-    flaky: true
 
   basic_material_app_ios__compile:
     description: >
@@ -72,7 +68,6 @@ tasks:
       app for iOS from Mac.
     stage: devicelab_ios
     required_agent_capabilities: ["has-ios-device"]
-    flaky: true
 
   basic_material_app_win__compile:
     description: >
@@ -80,7 +75,6 @@ tasks:
       app for Android from Windows.
     stage: devicelab_win
     required_agent_capabilities: ["windows"]
-    flaky: true
 
   flutter_gallery_android__compile:
     description: >
@@ -88,7 +82,6 @@ tasks:
       Gallery for Android from Linux.
     stage: devicelab
     required_agent_capabilities: ["linux/android"]
-    flaky: true
 
   flutter_gallery_ios__compile:
     description: >
@@ -96,7 +89,6 @@ tasks:
       Gallery for iOS from Mac.
     stage: devicelab_ios
     required_agent_capabilities: ["has-ios-device"]
-    flaky: true
 
   flutter_gallery_win__compile:
     description: >
@@ -104,7 +96,6 @@ tasks:
       Gallery for Android from Windows.
     stage: devicelab_win
     required_agent_capabilities: ["windows"]
-    flaky: true
 
   # Android on-device tests
 
@@ -132,7 +123,6 @@ tasks:
       Checks that external UIs work on Android.
     stage: devicelab
     required_agent_capabilities: ["has-android-device"]
-    flaky: true
 
   platform_interaction_test:
     description: >