FIX delete flag unused function

.pre-commit-config.yaml

@@ -20,5 +20,5 @@ repos:
       - id: cppcheck
         name: cppcheck
         require_serial: true
-        entry: cppcheck --enable=all --suppress=missingInclude --suppress=missingIncludeSystem --suppress=unusedFunction --inline-suppr -i mbed-os --std=c++14 --error-exitcode=1
+        entry: cppcheck --enable=all --suppress=missingInclude --suppress=missingIncludeSystem --inline-suppr -i mbed-os --std=c++14 --error-exitcode=1
         language: system