go/ssa: remove coretype_test.go

go/ssa/coretype_test.go was copied to internal/typeparams/coretype_test.go.
Removing the old copy.

Fixes error message in typeparams/coretype_test.go.

Change-Id: If5553fb75b580411ea4d24923b38f15cccf1f0ba
Reviewed-on: https://go-review.googlesource.com/c/tools/+/642156
Reviewed-by: Tim King <taking@google.com>
Reviewed-by: Robert Griesemer <gri@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Tim King <taking@google.com>

Author: Tim King

go/ssa/coretype_test.go

@@ -95,7 +95,7 @@ func TestCoreType(t *testing.T) {
 			got = ct.String()
 		}
 		if got != test.want {
-			t.Errorf("coreType(%s) = %v, want %v", test.expr, got, test.want)
+			t.Errorf("CoreType(%s) = %v, want %v", test.expr, got, test.want)
 		}
 	}
 }