presubmit: remove reserved field from InputProperties

This is followup for crrev.com/c/1877747

Bug: 1002153
Change-Id: I7f5e6f9be9e69ecfbaad75f531d5027ef20a3966
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1878847
Auto-Submit: Takuto Ikuta <tikuta@chromium.org>
Reviewed-by: Robbie Iannucci <iannucci@chromium.org>
Commit-Queue: Robbie Iannucci <iannucci@chromium.org>

recipes/recipe_modules/presubmit/properties.proto

@@ -10,8 +10,4 @@ message InputProperties {
   bool runhooks = 1;
   // Timeout for presubmit execution, in seconds.
   int32 timeout_s = 2;
-
-  // TODO(tikuta): remove this if this is not necessary.
-  reserved "vpython_spec_path";
-  reserved 3;
 }