nanobsd: Avoid unnecessary subshell execution

Mimic c99bb5747f ("nanobsd: minor formatting cleanup") and cleanup
_create_code_slice(), somehow I missed it when rebasing.

No functional change intended.

Fixes:		ecc039be7f ("nanobsd: Add a NO_ROOT build option")
MFC after:	3 days

tools/tools/nanobsd/legacy.sh

@@ -155,7 +155,7 @@ create_code_slice() {
 	) > ${NANO_OBJ}/_.cs 2>&1
 }
 
-_create_code_slice ( ) (
+_create_code_slice() {
 	pprint 2 "build code slice"
 	pprint 3 "log: ${NANO_OBJ}/_.cs"
 
@@ -181,7 +181,7 @@ _create_code_slice ( ) (
 	rm -f "${NANO_OBJ}/_.disk.part"
 
 	) > ${NANO_OBJ}/_.cs 2>&1
-)
+}
 
 create_diskimage() {
 	pprint 2 "build diskimage"