Remove unused org.apache.http.impl.client.cache requirement

The package is not used by the plugin and seems to be missing in the
platform anyway under some conditions, see bug 508321 (newer
org.apache.httpcomponents.httpclient_4.5.2 does NOT include the package,
org.apache.httpcomponents.httpclient_4.3.6 does).

Change-Id: Ida5d926a611812b5177af651b3cf22f1b2519e02
Signed-off-by: Andrey Loskutov <loskutov@gmx.de>

org.eclipse.jgit.http.apache/META-INF/MANIFEST.MF

@@ -20,7 +20,6 @@ Import-Package: org.apache.http;version="[4.3.0,5.0.0)",
  org.apache.http.conn.ssl;version="[4.3.0,5.0.0)",
  org.apache.http.entity;version="[4.3.0,5.0.0)",
  org.apache.http.impl.client;version="[4.3.0,5.0.0)",
- org.apache.http.impl.client.cache;version="[4.3.0,5.0.0)",
  org.apache.http.impl.conn;version="[4.3.0,5.0.0)",
  org.apache.http.params;version="[4.3.0,5.0.0)",
  org.eclipse.jgit.nls;version="[4.7.0,4.8.0)",