@Override
	public Symbol getExternalSymbol(String name) {
		lock.acquire();
		try {
			SymbolIterator it = getExternalSymbols(name);
			if (it.hasNext()) {
				return it.next();
			}
			return null;
		}
		finally {
			lock.release();
		}
	}
Called by the NamespaceManager when a namespace is removed; remove all symbols that have the
given namespace ID.

@param namespaceID ID of namespace being removed
Ghidra/Framework/SoftwareModeling/src/main/java/ghidra/program/database/symbol/SymbolManager.java