http.bzl: Use syntactically correct checksums in examples

The Starlark version of http_archive comes with some documenting examples,
that also provide the sha256 parameter, as is best practice. However, the
example value is not syntactically a sha256 sum (in fact, it has to the
length of a sha1 sum) which can be irritating. Therefore, replace it with
a proper sha256 sum (that of the empty string).

Change-Id: I6ea7b4aa0f8b3603b670400650ca64cd8082cf61
PiperOrigin-RevId: 245410913
diff --git a/tools/build_defs/repo/http.bzl b/tools/build_defs/repo/http.bzl
index 4b763e2..28acc51 100644
--- a/tools/build_defs/repo/http.bzl
+++ b/tools/build_defs/repo/http.bzl
@@ -269,7 +269,7 @@
   http_archive(
       name = "my_ssl",
       urls = ["http://example.com/openssl.zip"],
-      sha256 = "03a58ac630e59778f328af4bcc4acb4f80208ed4",
+      sha256 = "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855",
       build_file = "@//:openssl.BUILD",
   )
   ```
@@ -321,7 +321,7 @@
   http_file(
       name = "my_deb",
       urls = ["http://example.com/package.deb"],
-      sha256 = "03a58ac630e59778f328af4bcc4acb4f80208ed4",
+      sha256 = "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855",
   )
   ```
 
@@ -366,7 +366,7 @@
   http_jar(
       name = "my_ssl",
       url = "http://example.com/openssl-0.2.jar",
-      sha256 = "03a58ac630e59778f328af4bcc4acb4f80208ed4",
+      sha256 = "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855",
   )
   ```