WebUI: Remove |input_files| from |inputs| in generate_grd.gni.

Currently the contents of the generated grd file do not depend on the
contents of each individiual |input_files| member, so such files
should not be declared as |inputs|.

Bug: 1132403
Change-Id: I6ccdcee19fae5304454561fa2cbf19eb770e6865
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2468377Reviewed-by: Rebekah Potter <rbpotter@chromium.org>
Commit-Queue: Rebekah Potter <rbpotter@chromium.org>
Commit-Queue: dpapad <dpapad@chromium.org>
Auto-Submit: dpapad <dpapad@chromium.org>
Cr-Commit-Position: refs/heads/master@{#816705}

ui/webui/resources/tools/generate_grd.gni

@@ -11,10 +11,6 @@ template("generate_grd") {
     }
 
     inputs = invoker.manifest_files
-    if (defined(invoker.input_files)) {
-      inputs += invoker.input_files
-    }
-
     outputs = [ invoker.out_grd ]
 
     args = [