Remove hardcoded plugin name that does not match jar from BUCK build

The BUCK build generates a x-docs.jar (with dash), which nicely
matches the repository name x-docs (with dash). However, when loading
the jar, the plugin shows up as xdocs (no dash).

To harmonize names, we drop the hardcoded dashless plugin name. This
makes naming more consistent, helps with automated system tests, and
also allows people to load the plugin under whatever name they choose
to.

Change-Id: I05ffc0b4555d9fd02784a389f8d6725df060999f

BUCK

diff --git a/BUCK b/BUCK
index 5003c2a..980f082 100644
--- a/BUCK
+++ b/BUCK
@@ -17,7 +17,6 @@
   resources = glob(['src/main/**/*']),
   gwt_module = MODULE,
   manifest_entries = [
-    'Gerrit-PluginName: xdocs',
     'Gerrit-ApiType: plugin',
     'Gerrit-ApiVersion: 2.12-SNAPSHOT',
     'Gerrit-HttpModule: com.googlesource.gerrit.plugins.xdocs.HttpModule',