I've gone through the Weld code coverage report (including TCK, tests, arquillian tests) and discovered bunch of likely useless (not called) classes and some pieces of code. Classes are:

org.jboss.weld.bootstrap.ExtensionBeanDeployerEnvironment
org.jboss.weld.context.ForwardingWeldCreationalContext
org.jboss.weld.context.beanstore.ForwardingNamingScheme
org.jboss.weld.context.beanstore.http.LazyCyclicSessionBeanStore
org.jboss.weld.exceptions.NullableDependencyException
org.jboss.weld.executor.TaskPerItemTaskFactory
org.jboss.weld.injection.ForwardingInjectionTarget
org.jboss.weld.interceptor.util.InterceptorMetadataException
org.jboss.weld.manager.RemoveMetadataWrapperFunction
org.jboss.weld.resolution.ForwardingInterceptorResolvable
org.jboss.weld.resources.SharedObjectFacade
org.jboss.weld.serialization.NoopSerializableHolder
org.jboss.weld.util.annotated.ForwardingAnnotatedConstructor
org.jboss.weld.util.annotated.ForwardingAnnotatedField
org.jboss.weld.util.annotated.ForwardingAnnotatedParameter
org.jboss.weld.util.annotated.ForwardingWeldAnnotation
org.jboss.weld.util.annotated.ForwardingWeldConstructor
org.jboss.weld.util.annotated.ForwardingWeldField
org.jboss.weld.util.annotated.ForwardingWeldMember (called, but only in classes mentioned in this list)
org.jboss.weld.util.annotated.ForwardingWeldMethod
org.jboss.weld.util.annotated.ForwardingWeldParameter
org.jboss.weld.util.collections.ArrayListSupplier
org.jboss.weld.util.collections.ArraySetSupplier
org.jboss.weld.util.collections.ConcurrentHashSetSupplier
org.jboss.weld.util.collections.CopyOnWriteArrayListSupplier
org.jboss.weld.util.collections.DefaultValueMap
org.jboss.weld.util.collections.SetView
org.jboss.weld.util.dom.NodeListIterable
org.jboss.weld.util.dom.NodeListIterator (called in the class above only)
org.jboss.weld.util.reflection.ClassLoaderFunction

Following pieces of code could be likely also removed:

• org.jboss.weld.injection.DynamicInjectionPoint#DynamicInjectionPoint(org.jboss.weld.injection.SLSBInvocationInjectionPoint, java.lang.String)
• org.jboss.weld.injection.DynamicInjectionPoint#readResolve
• org.jboss.weld.util.Beans#findInterceptorBindingConflicts - not sure but I guess the if statement is useless in for cycle
• org.jboss.weld.util.bean.WrappedBeanHolder - this class is used in static classes, which are not likely referenced anywhere.
• org.jboss.weld.util.bytecode.DescriptorUtils#descriptorStringToParameterArray
• org.jboss.weld.util.bytecode.DescriptorUtils#isWide(java.lang.Class<?>)
• org.jboss.weld.util.bytecode.DescriptorUtils#getConstructorDescriptor
• org.jboss.weld.util.bytecode.DescriptorUtils#getMethodDescriptor(java.lang.reflect.Method)

All changes are available https://github.com/tremes/core/commit/6e7a4595d8b1cf4eaf1dee9a8924c4f1ee9e0cd2, but I still need to test it properly.