treewide: fix unnecessary $ on arithmetic variables

This should fix shellcheck warning SC2004.

shell-completion/bash/busctl

@@ -139,7 +139,7 @@ _busctl() {
         fi
     done
 
-    n=$(($COMP_CWORD - $i))
+    n=$((COMP_CWORD - i))
 
     if [[ -z ${verb-} ]]; then
         comps=${VERBS[*]}

shell-completion/bash/portablectl

@@ -78,7 +78,7 @@ _portablectl() {
         fi
     done
 
-    n=$(($COMP_CWORD - $i))
+    n=$((COMP_CWORD - i))
 
     if [[ -z ${verb-} ]]; then
         comps=${VERBS[*]}

test/units/testsuite-35.sh

@@ -591,7 +591,7 @@ test_ambient_caps() {
     # CAP_CHOWN | CAP_KILL
     MASK=$(((1 << 0) | (1 << 5)))
 
-    if [ $(("$BND" & "$MASK")) -ne "$MASK" ] ; then
+    if [ $((BND & MASK)) -ne "$MASK" ] ; then
         echo "CAP_CHOWN or CAP_KILL not available in bounding set, skipping test." >&2
         return
     fi

test/units/testsuite-57-short-lived.sh

@@ -4,7 +4,7 @@ set -ex
 
 if [ -f /tmp/testsuite-57.counter ] ; then
     read -r counter < /tmp/testsuite-57.counter
-    counter=$(("$counter" + 1))
+    counter=$((counter + 1))
 else
     counter=0
 fi

test/units/testsuite-59.sh

@@ -116,13 +116,13 @@ LEAVE=0
 
 function reload() {
     systemd-notify --reloading --status="Adding 11 to exit status"
-    EXIT_STATUS=\$((\$EXIT_STATUS + 11))
+    EXIT_STATUS=\$((EXIT_STATUS + 11))
     systemd-notify --ready --status="Back running"
 }
 
 function leave() {
     systemd-notify --stopping --status="Adding 7 to exit status"
-    EXIT_STATUS=\$((\$EXIT_STATUS + 7))
+    EXIT_STATUS=\$((EXIT_STATUS + 7))
     LEAVE=1
     return 0
 }
@@ -138,7 +138,7 @@ while [ \$LEAVE = 0 ] ; do
 done
 
 systemd-notify --status="Adding 3 to exit status"
-EXIT_STATUS=\$((\$EXIT_STATUS + 3))
+EXIT_STATUS=\$((EXIT_STATUS + 3))
 exit \$EXIT_STATUS
 EOF