go.tools/.hgignore: don't ignore test-generated files, clean them up.

(Includes rollback of CL 83680043.)

LGTM=gri
R=gri
CC=golang-codereviews, rsc
https://golang.org/cl/86430045

.hgignore

@@ -1,4 +1,3 @@
-# Add no patterns to .hgignore except for files generated by 'go build'/'go test'.
+# Add no patterns to .hgignore except for files generated by the build.
 syntax:glob
 last-change
-*.got

oracle/oracle_test.go

@@ -234,6 +234,7 @@ func TestOracle(t *testing.T) {
 			continue
 		}
 		defer gotfh.Close()
+		defer os.Remove(got)
 
 		// Run the oracle on each query, redirecting its output
 		// and error (if any) to the foo.got file.

refactor/eg/eg_test.go

@@ -119,6 +119,7 @@ func Test(t *testing.T) {
 		if err := eg.WriteAST(iprog.Fset, got, file); err != nil {
 			t.Error(err)
 		}
+		defer os.Remove(got)
 
 		// Compare foo.got with foo.golden.
 		var cmd *exec.Cmd