Format shell scripts with shfmt.

All changes in this patch were performed automatically with `shfmt` with
configuration flags specified in `.pre-commit-config.yaml`.

In addition to fixing whitespace the roundtrip through shfmt's AST also
transforms command substitutions

    `cmd`
    # becomes
    $(cmd)

and some redirects

    >&2 echo "msg"
    # becomes
    echo >&2 "msg"

testing/scripts/diff-remove-openclose-timestamps

@@ -3,10 +3,10 @@
 # Replace timestamps in the #start/end markers in logs.
 
 # Get us "modern" regexps with sed.
-if [ `uname` == "Linux" ]; then
-   sed="sed -r"
+if [ $(uname) == "Linux" ]; then
+    sed="sed -r"
 else
-   sed="sed -E"
+    sed="sed -E"
 fi
 
 $sed 's/^ *#(open|close).(19|20)..-..-..-..-..-..$/#\1 XXXX-XX-XX-XX-XX-XX/g'