Remove generation of the version file

The github-pugin.jar-version is generated automatically
from the Gerrit-CI's jobs and should not be created by
the plugin's Bazel build.

Change-Id: I262146669b089efe755e48f2a0cbb39d790d5dca

BUILD

diff --git a/BUILD b/BUILD
index 41bb112..919c453 100644
--- a/BUILD
+++ b/BUILD
@@ -4,7 +4,6 @@
     name = "github",
     srcs = [
         ":github-plugin",
-        ":github-plugin-version",
         ":github-oauth",
     ],
     outs = ["github.zip"],
@@ -18,13 +17,6 @@
     cmd = "cp $< $@",
 )
 
-genrule2(
-    name = "github-plugin-version",
-    srcs = [":github-plugin"],
-    outs = ["github-plugin.jar-version"],
-    cmd = "jar xvf $< META-INF/MANIFEST.MF; cat META-INF/MANIFEST.MF | grep Implementation-Version | cut -d ':' -f 2 | xargs > $@",
-)
-
 genrule(
     name = "github-plugin",
     srcs = ["//plugins/github/github-plugin"],