message: micro: fix unused-variable-warning
  When TF_LITE_STRIP_ERROR_STRINGS is undefined, TF_LITE_REPORT_ERROR is
  expanded to the empty string. This left some string variables, which had
  been added to avoid using %c in format string, as unused.
diff: @@ -21,6 +21,8 @@ namespace tflite {
  namespace {
  +// Returns a character representing a numbered buffer
  +// for GreedyMemoryPlanner::PrintMemoryPlan()
  char GetOrdinalCharacter(int i) {
  if (i < 10) {
  return '0' + i;
  @@ -332,12 +334,14 @@ void GreedyMemoryPlanner::PrintMemoryPlan(ErrorReporter* error_reporter) {
  CalculateOffsetsIfNeeded();
  for (int i = 0; i < buffer_count_; ++i) {
  +#ifndef TF_LITE_STRIP_ERROR_STRINGS
  char s[] = {GetOrdinalCharacter(i), 0};
  TF_LITE_REPORT_ERROR(
  error_reporter,
  "%s (id=%d): size=%d, offset=%d, first_used=%d last_used=%d", s, i,
  requirements_[i].size, buffer_offsets_[i],
  requirements_[i].first_time_used, requirements_[i].last_time_used);
  +#endif
  }
  constexpr int kLineWidth = 80;
  @@ -386,8 +390,7 @@ void GreedyMemoryPlanner::PrintMemoryPlan(ErrorReporter* error_reporter) {
  }
  line[kLineWidth] = 0;
  - char padding[] = {t < 100 ? ' ' : '\0', t < 10 ? ' ' : '\0', '\0'};
  - TF_LITE_REPORT_ERROR(error_reporter, "%s%d: %s (%dk)", padding, t,
  + TF_LITE_REPORT_ERROR(error_reporter, "%s%d: %s (%dk)", t < 10 ? " " : "", t,
  (const char*)line, (memory_use + 1023) / 1024);
  }
  }
  