[mlir] Remove EDSC BlockBuilder, BlockHandle and related functionality

Callback-based constructions of blocks where the body is populated in the same
function as the block creation is a natural extension of callback-based loop
construction. They provide more concise and simple APIs than EDSC BlockBuilder
at less than 20% infrastructural code cost, and are compatible with
ScopedContext. BlockBuilder, Blockhandle and related functionality has been
deprecated, remove them.

Differential Revision: https://reviews.llvm.org/D82015