Don't echo command from run_and_expect_silence. (#2405)

Some commands, like our errcheck command, are very long. When we echo these both
before and after running them, it can obscure what is often a single-line
failure message. Removing the echo after failure makes it easier to spot the
real failure message.

test.sh

@@ -60,7 +60,6 @@ function run_and_expect_silence() {
 
   # Fail if result_file is nonempty.
   if [ -s ${result_file} ]; then
-    echo "[!] FAILURE: $@"
     FAILURE=1
   fi
   rm ${result_file}