replaced ./cargo with cargo in build docs (solana-labs#29375)

docs/build-cli-usage.sh

@@ -2,17 +2,16 @@
 set -e
 
 cd "$(dirname "$0")"
-cargo=../cargo
 
 # shellcheck source=ci/rust-version.sh
 source ../ci/rust-version.sh stable
 
 : "${rust_stable:=}" # Pacify shellcheck
 
 # pre-build with output enabled to appease Travis CI's hang check
-"$cargo" build -p solana-cli
+cargo build -p solana-cli
 
-usage=$("$cargo" stable -q run -p solana-cli -- -C ~/.foo --help | sed -e 's|'"$HOME"'|~|g' -e 's/[[:space:]]\+$//')
+usage=$(cargo -q run -p solana-cli -- -C ~/.foo --help | sed -e 's|'"$HOME"'|~|g' -e 's/[[:space:]]\+$//')
 
 out=${1:-src/cli/usage.md}
 
@@ -40,6 +39,6 @@ in_subcommands=0
 while read -r subcommand rest; do
   [[ $subcommand == "SUBCOMMANDS:" ]] && in_subcommands=1 && continue
   if ((in_subcommands)); then
-      section "$("$cargo" stable -q run -p solana-cli -- help "$subcommand" | sed -e 's|'"$HOME"'|~|g' -e 's/[[:space:]]\+$//')" "####" >> "$out"
+      section "$(cargo -q run -p solana-cli -- help "$subcommand" | sed -e 's|'"$HOME"'|~|g' -e 's/[[:space:]]\+$//')" "####" >> "$out"
   fi
 done <<<"$usage">>"$out"