Revert "Add headers to headermap action inputs (#888)"

This reverts commit 3558642.

rules/hmap.bzl

@@ -32,16 +32,9 @@ def _make_hmap(actions, headermap_builder, output, namespace, hdrs_lists):
     args.set_param_file_format(format = "multiline")
     args.use_param_file("@%s")
 
-    headers = [
-        header
-        for header_list in hdrs_lists
-        for header in header_list
-    ]
-
     actions.run(
         mnemonic = "HmapCreate",
         arguments = [args],
-        inputs = headers,
         executable = headermap_builder,
         outputs = [output],
     )