test/notmuch-test: simple streamlining

A few simple things that applies well to test/notmuch-test.sh

- Shell does pathname expansion also without doing `echo ...` in subshell.

- Redirections >/dev/null 2>/dev/null hide (improbable but) potential
  serious errors; adding -f to rm instead.

- Inter-file capitalization consistency in comments.

- Unnecesary space removal.

test/notmuch-test

@@ -17,12 +17,12 @@ fi
 
 cd "$(dirname "$0")"
 
-TESTS=${NOTMUCH_TESTS:-`echo T[0-9][0-9][0-9]-*.sh`}
+TESTS=${NOTMUCH_TESTS:-T[0-9][0-9][0-9]-*.sh}
 
 # Clean up any results from a previous run
-rm -r test-results >/dev/null 2>/dev/null
+rm -rf test-results
 
-# test for timeout utility
+# Test for timeout utility
 if command -v timeout >/dev/null; then
     TEST_TIMEOUT_CMD="timeout 2m"
     echo "INFO: using 2 minute timeout for tests"