Build: Revert "Pin Opera 36 to macOS"

I'm staging this in a temporary branch to help BrowserStack Support
diagnose the issue.

This reverts commit 1930124:
> The BrowserStack VMs for Opera on Win7,8,10 are currently broken.

build/browserstack-full.json

@@ -5,90 +5,6 @@
   "exit_with_fail": true,
   "timeout": 600,
   "browsers": [
-    "firefox_45",
-    "firefox_78",
-    "firefox_previous",
-    "firefox_current",
-    "ie_9",
-    "ie_10",
-    "ie_11",
-    "edge_15",
-    "edge_18",
-    "edge_previous",
-    "edge_current",
-    "safari_9.1",
-    "safari_10.1",
-    "safari_11.1",
-    "safari_12.1",
-    "safari_13.1",
-    "safari_current",
-    {
-
-      "browser": "opera",
-      "browser_version": "36.0",
-      "device": null,
-      "os": "OS X",
-      "os_version": "Sierra"
-    },
-    "opera_previous",
-    "opera_current",
-    "chrome_58",
-    "chrome_previous",
-    "chrome_current",
-    {
-      "device": "Samsung Galaxy S20",
-      "real_mobile": true,
-      "os": "android",
-      "os_version": "10.0"
-    },
-    {
-      "device": "iPhone 7",
-      "real_mobile": true,
-      "os": "ios",
-      "os_version": "10"
-    },
-    {
-      "device": "iPhone SE",
-      "real_mobile": true,
-      "os": "ios",
-      "os_version": "11"
-    },
-    {
-      "device": "iPhone XR",
-      "real_mobile": true,
-      "os": "ios",
-      "os_version": "12"
-    }
-  ],
-  "@browsers_disabled": [
-    {
-      "@ref": [
-        "https://github.com/browserstack/browserstack-runner/issues/245",
-        "Android 4, Android 5, Android 6"
-      ]
-    },
-    {
-      "@ref": [
-        "https://github.com/browserstack/browserstack-runner/issues/226",
-        "Android 7-10",
-        "iOS 13, 14"
-      ]
-    },
-    {
-      "device": "Samsung Galaxy S7",
-      "real_mobile": true,
-      "os": "android",
-      "os_version": "6.0"
-    },
-    {
-      "device": null,
-      "os": "ios",
-      "os_version": "13"
-    },
-    {
-      "device": null,
-      "os": "ios",
-      "os_version": "14"
-    }
+    "opera_36"
   ]
 }