Removed obsoleted main-class attribute from jdt.core manifest (eclips…

…e-jdt#181)

jdt.core can't be used anymore as self containing Java compiler library,
it is now org.eclipse.jdt.core.compiler.batch.

See eclipse-jdt#181

org.eclipse.jdt.core/META-INF/MANIFEST.MF

@@ -1,5 +1,4 @@
 Manifest-Version: 1.0
-Main-Class: org.eclipse.jdt.internal.compiler.batch.Main
 Bundle-ManifestVersion: 2
 Bundle-Name: %pluginName
 Bundle-SymbolicName: org.eclipse.jdt.core; singleton:=true