[mlir] Remove eliminateBlockingAwaitOps option in AsyncToAsyncRuntime pass

Remove the eliminateBlockingAwaitOps option in AsyncToAsyncRuntime pass

Today the AsyncToAsyncRuntime pass does two things: one is converting normal funcs with async ops to coroutine cfg; the other is lowering high level async operations to async.coro and async.runtime operations. This patch removes the converting step from AsyncToAsyncRuntime pass.

In the next step we will create a new asyncfication pass for converting normal funcs to the newly added async.func operation.

Reviewed By: ezhulenev

Differential Revision: https://reviews.llvm.org/D137282