Revert "build: update to yarn@1.21.1" (#34402)

This reverts commit f029af50820765019413fa319330830306b80d6a while we investigate
some failures on master on Circle CI. Currently the Windows tests and the
"test-ivy-aot" jobs are red because of incompatible yarn versions.

PR Close #34402

WORKSPACE

@@ -41,9 +41,17 @@ node_repositories(
     node_version = "10.16.0",
     package_json = ["//:package.json"],
     yarn_repositories = {
-        "1.21.1": ("yarn-v1.21.1.tar.gz", "yarn-v1.21.1", "d1d9f4a0f16f5ed484e814afeb98f39b82d4728c6c8beaafb5abc99c02db6674"),
+        "1.17.3": ("yarn-v1.17.3.tar.gz", "yarn-v1.17.3", "e3835194409f1b3afa1c62ca82f561f1c29d26580c9e220c36866317e043c6f3"),
     },
-    yarn_version = "1.21.1",
+    # yarn 1.13.0 under Bazel has a regression on Windows that causes build errors on rebuilds:
+    # ```
+    # ERROR: Source forest creation failed: C:/.../fyuc5c3n/execroot/angular/external (Directory not empty)
+    # ```
+    # See https://github.com/angular/angular/pull/29431 for more information.
+    # It possible that versions of yarn past 1.13.0 do not have this issue, however, before
+    # advancing this version we need to test manually on Windows that the above error does not
+    # happen as the issue is not caught by CI.
+    yarn_version = "1.17.3",
 )
 
 yarn_install(