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/vivid

@@ -3,7 +3,7 @@
 # ➜ https://github.com/sharkdp/vivid
 # 💡Use command `vivid themes` to see available themes
 
-if (command -v vivid &>/dev/null); then
+if command -v vivid &>/dev/null; then
   THEME=tokyonight-moon
   LS_COLORS="$(vivid generate ${THEME})"
   export LS_COLORS