dashboard: add some "exp" trybots back, clean up some config

Fixes golang/go#30781

Change-Id: I2672ca2949837c3cfe8fa6bd8011d1b9b43cca03
Reviewed-on: https://go-review.googlesource.com/c/build/+/167640
Reviewed-by: Bryan C. Mills <bcmills@google.com>
diff --git a/dashboard/builders_test.go b/dashboard/builders_test.go
index 130e4dd..45c8c6e 100644
--- a/dashboard/builders_test.go
+++ b/dashboard/builders_test.go
@@ -155,6 +155,19 @@
 				"windows-amd64-2016",
 			},
 		},
+		{
+			repo:   "exp",
+			branch: "master",
+			want: []string{
+				"freebsd-amd64-12_0",
+				"linux-386",
+				"linux-amd64",
+				"linux-amd64-race",
+				"openbsd-amd64-64",
+				"windows-386-2008",
+				"windows-amd64-2016",
+			},
+		},
 	}
 	for i, tt := range tests {
 		if tt.branch == "" || tt.repo == "" {
@@ -398,6 +411,10 @@
 		{b("linux-amd64-longtest", "net"), onlyPost},
 		{b("linux-amd64-longtest@go1.12", "go"), onlyPost},
 		{b("linux-amd64-longtest@go1.12", "net"), none},
+
+		// Experimental exp repo.
+		{b("linux-amd64", "exp"), both},
+		{b("windows-386-2008", "exp"), both},
 	}
 	for _, tt := range tests {
 		t.Run(tt.br.testName, func(t *testing.T) {