Barclays Plc said it is quitting the majority of its commodities businesses to join a retreat from the area by a number of banks as tougher regulations make it less profitable. Barclays will exit from most of its metals, energy and agricultural trading but remain trading precious metals, some oil and gas instruments, and index products, the bank said on Tuesday. The smaller business will be focused on electronic execution, it said. Barclays is expected to next month unveil a wider reduction in the size of its investment bank…