t/*: some cleanups so switching between redo and minimal/do works.

Because the two programs use separate state databases, it helps if we
clean up some temp files between runs.  Otherwise they might think you
created some targets "by hand" and refuse to rebuild them.

t/102-empty/silencetest.do

@@ -1,3 +1,7 @@
+# This may have been leftover from a previous run, when switching
+# between "real" redo and minimal/do, so clean it up.
+rm -f silence
+
 echo 'echo hello' >silence.do
 redo silence
 [ -e silence ] || exit 55

t/102-empty/touchtest.do

@@ -1,3 +1,7 @@
+# This may have been leftover from a previous run, when switching
+# between "real" redo and minimal/do, so clean it up.
+rm -f touch1
+
 echo 'echo hello' >touch1.do
 redo touch1
 [ -e touch1 ] || exit 55