shell/caucase.sh,.shellcheckrc: Make shellcheck happy.

Silence the warning about "local" not being POSIX, as many shells implement
it.
Resolve the other watnings, related to now-useless "x" prefixes in [
arguments.

.shellcheckrc

 enable=avoid-nullary-conditions
 enable=deprecate-which
+disable=SC3043 # In POSIX sh, 'local' is undefined.

shell/caucase.sh

@@ -470,9 +470,9 @@ EOF
       "$url/crt/renew/"
   )"; then
     if [ \
-      "x$(printf '%s\n' "$newcrtdata" | head -n 1)" \
+      "$(printf '%s\n' "$newcrtdata" | head -n 1)" \
       = \
-      'x-----BEGIN CERTIFICATE-----' \
+      '-----BEGIN CERTIFICATE-----' \
     ]; then
       if checkCertificateMatchesKey "$newcrtdata" "$newkeydata"; then
         writeCertKey "$newcrt" "$newcrtdata" "$newkey" "$newkeydata"
@@ -875,7 +875,7 @@ EOF
         --version)
           # shellcheck disable=SC2016
           version='$Format:%H$'
-          if [ "x$(echo "$version" | base64)" = 'xJEZvcm1hdDolSCQK' ]; then
+          if [ "$(echo "$version" | base64)" = 'JEZvcm1hdDolSCQK' ]; then
             if command -v git > /dev/null; then
               version="$(git describe --tags --dirty --always --long)"
             else
@@ -1031,7 +1031,7 @@ EOF
           crt_path="$2"
           shift 2
           crt_dir="$(dirname "$crt_path")"
-          if [ "x$crt_path" = 'x-' ]; then
+          if [ "$crt_path" = '-' ]; then
             # stdin & stdout
             :
           elif [ -w "$crt_path" ] && [ -r "$crt_path" ]; then
@@ -1047,7 +1047,7 @@ EOF
           fi
           crt="$(getCertificate "${ca_anon_url}/${mode_path}" "$csr_id")" \
           || return
-          if [ "x$crt_path" = 'x-' ]; then
+          if [ "$crt_path" = '-' ]; then
             printf '%s\n' "$crt"
           else
             if [ -e "$crt_path" ]; then
@@ -1105,7 +1105,7 @@ EOF
           csr="$(
             getCertificateSigningRequest "${ca_anon_url}/${mode_path}" "$csr_id"
           )" || return
-          if [ "x$csr_path" = 'x-' ]; then
+          if [ "$csr_path" = '-' ]; then
             printf '%s\n' "$csr"
           else
             printf '%s\n' "$csr" > "$csr_path"
@@ -1384,7 +1384,7 @@ EOF
     fi
     echo 'Success'
   }
-  if [ "$#" -gt 0 ] && [ "x$1" = 'x--test' ]; then
+  if [ "$#" -gt 0 ] && [ "$1" = '--test' ]; then
     if [ "$#" -le 2 ]; then
       _test "${2:-localhost:8000}"
     else