Bazel: Stop unsigning jgit libraries

This change deletes the last GWT related hack in build tool chain:
unsigning of JGit libraries to prevent security exception after adding
new class to the existing org.eclipse.jgit.diff package. Instead of
adding new ReplaceEdit class to this package, move the class to its own
gerrit top level package.

My understanding was, that we have done unsigning acrobatic to support
deserialization and JSON deserialization for GWT UI. Particularly these
two classes:

* EditDeserializer.java
* Edit_JsonSerializer.java

Right now I do not see why this couldn't be done in gerrit own package.
In any event, we do not intend to backport this change to other stable
branches but only apply it to branches where GWT UI was removed.

Change-Id: I3be17767ed495bb1b8c5c2ce4ca1574c865b2fba

tools/download_file.py

@@ -81,7 +81,6 @@ opts.add_option('-u', help='URL to download')
 opts.add_option('-v', help='expected content SHA-1')
 opts.add_option('-x', action='append', help='file to delete from ZIP')
 opts.add_option('--exclude_java_sources', action='store_true')
-opts.add_option('--unsign', action='store_true')
 args, _ = opts.parse_args()
 
 root_dir = args.o
@@ -140,18 +139,6 @@ if args.exclude_java_sources:
         print('error opening %s: %s' % (cache_ent, err), file=stderr)
         exit(1)
 
-if args.unsign:
-    try:
-        with ZipFile(cache_ent, 'r') as zf:
-            for n in zf.namelist():
-                if (n.endswith('.RSA')
-                   or n.endswith('.SF')
-                   or n.endswith('.LIST')):
-                    exclude.append(n)
-    except (BadZipfile, LargeZipFile) as err:
-        print('error opening %s: %s' % (cache_ent, err), file=stderr)
-        exit(1)
-
 safe_mkdirs(path.dirname(args.o))
 if exclude:
     try: