perf: remove unnecessary subshells in command -v checks

Replace 'if (command -v x &>/dev/null); then' with
'if command -v x &>/dev/null; then' across completion.d, rc.d and
profile.d. Parentheses forced a subshell fork for every 'if' check,
which is unnecessary overhead since command -v runs fine in the
current shell.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

rc.d/startx

@@ -13,12 +13,12 @@ if [[ -z "${DISPLAY}" && $(id -u) -ge 1000 ]] ; then
             3) VT=vt3 ;;
         esac
 
-        if ( command -v ck-launch-session &> /dev/null )
+        if command -v ck-launch-session &> /dev/null
         then
             EXEC="exec ck-launch-session"
         fi
 
-        if ( command -v startx &> /dev/null )
+        if command -v startx &> /dev/null
         then
             ${EXEC} startx 1> ~/.log/xsession-errors 2>&1 -- "${VT}"
         fi