Disable non-conformant configs on official builds.

Bug: angleproject:2950
Change-Id: Idcb907587abea99ff6b1c2cbe6bb327af0222b10
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1506007
Reviewed-by: Courtney Goeltzenleuchter <courtneygo@google.com>
Reviewed-by: Tim Van Patten <timvp@google.com>
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>

gni/angle.gni

@@ -82,8 +82,8 @@ declare_args() {
     # Enable Vulkan GPU trace event capability
     angle_enable_vulkan_gpu_trace_events = false
 
-    # Disallow non-conformant configurations
-    angle_vulkan_conformant_configs_only = false
+    # Disallow non-conformant configurations in official builds.
+    angle_vulkan_conformant_configs_only = is_official_build
   }
 }