Drop shebang from upload_doc.sh (#408)

This file isn't directly executable in any of its forms:
* When checked into the repository, it is a template
* When installed by gz-cmake, it is still a template
* When expanded in downstream packages, it isn't explicitly given
  executable permission, requiring an explicit interpreter invocation

Additionally, the usage for this script instructs the user to explicitly
provide the interpreter. To avoid misleading users and linters into
believing that this file should be executed directly, drop the
(currently unused) shebang.

Signed-off-by: Scott K Logan <[email protected]>

cmake/upload_doc.sh.in

@@ -1,5 +1,3 @@
-#!/bin/sh
-
 echo "Usage: sh upload_doc.sh [y/n]"
 echo "  Optional [y/n] argument indicates whether to upload the docs to S3 automatically."