Tweak lock file to pull in only one React version

Yarn deps can be a bit fiddly when targeting specific versions. This tweaks the
lock file to only pull in a single React version.

For others who may need to do something like this again, I recommend deleting
specific package entries from `yarn.lock` and re-running `yarn install`. That
should make it pick the right thing while also leaving other packages as they
were.

yarn.lock

@@ -7374,17 +7374,7 @@ react-dom@^15.6.0:
     object-assign "^4.1.0"
     prop-types "^15.5.10"
 
-react-dom@^16.4.2:
-  version "16.8.6"
-  resolved "https://registry.yarnpkg.com/react-dom/-/react-dom-16.8.6.tgz#71d6303f631e8b0097f56165ef608f051ff6e10f"
-  integrity sha512-1nL7PIq9LTL3fthPqwkvr2zY7phIPjYrT0jp4HjyEQrEROnw4dG41VVwi/wfoCneoleqrNX7iAD+pXebJZwrwA==
-  dependencies:
-    loose-envify "^1.1.0"
-    object-assign "^4.1.1"
-    prop-types "^15.6.2"
-    scheduler "^0.13.6"
-
-react-dom@^16.9.0:
+react-dom@^16.4.2, react-dom@^16.9.0:
   version "16.9.0"
   resolved "https://registry.yarnpkg.com/react-dom/-/react-dom-16.9.0.tgz#5e65527a5e26f22ae3701131bcccaee9fb0d3962"
   integrity sha512-YFT2rxO9hM70ewk9jq0y6sQk8cL02xm4+IzYBz75CQGlClQQ1Bxq0nhHF6OtSbit+AIahujJgb/CPRibFkMNJQ==
@@ -7448,17 +7438,7 @@ react@^15.6.0:
     object-assign "^4.1.0"
     prop-types "^15.5.10"
 
-react@^16.4.2:
-  version "16.8.6"
-  resolved "https://registry.yarnpkg.com/react/-/react-16.8.6.tgz#ad6c3a9614fd3a4e9ef51117f54d888da01f2bbe"
-  integrity sha512-pC0uMkhLaHm11ZSJULfOBqV4tIZkx87ZLvbbQYunNixAAvjnC+snJCg0XQXn9VIsttVsbZP/H/ewzgsd5fxKXw==
-  dependencies:
-    loose-envify "^1.1.0"
-    object-assign "^4.1.1"
-    prop-types "^15.6.2"
-    scheduler "^0.13.6"
-
-react@^16.9.0:
+react@^16.4.2, react@^16.9.0:
   version "16.9.0"
   resolved "https://registry.yarnpkg.com/react/-/react-16.9.0.tgz#40ba2f9af13bc1a38d75dbf2f4359a5185c4f7aa"
   integrity sha512-+7LQnFBwkiw+BobzOF6N//BdoNw0ouwmSJTEm9cglOOmsg/TMiFHZLe2sEoN5M7LgJTj9oHH0gxklfnQe66S1w==
@@ -7893,14 +7873,6 @@ sax@^1.2.4:
   resolved "https://registry.yarnpkg.com/sax/-/sax-1.2.4.tgz#2816234e2378bddc4e5354fab5caa895df7100d9"
   integrity sha512-NqVDv9TpANUjFm0N8uM5GxL36UgKi9/atZw+x7YFnQ8ckwFGKrl4xX4yWtrey3UJm5nP1kUbnYgLopqWNSRhWw==
 
-scheduler@^0.13.6:
-  version "0.13.6"
-  resolved "https://registry.yarnpkg.com/scheduler/-/scheduler-0.13.6.tgz#466a4ec332467b31a91b9bf74e5347072e4cd889"
-  integrity sha512-IWnObHt413ucAYKsD9J1QShUKkbKLQQHdxRyw73sw4FN26iWr3DY/H34xGPe4nmL1DwXyWmSWmMrA9TfQbE/XQ==
-  dependencies:
-    loose-envify "^1.1.0"
-    object-assign "^4.1.1"
-
 scheduler@^0.15.0:
   version "0.15.0"
   resolved "https://registry.yarnpkg.com/scheduler/-/scheduler-0.15.0.tgz#6bfcf80ff850b280fed4aeecc6513bc0b4f17f8e"