Revert "[mlir] Add linalg.fill bufferization conversion"

This reverts commit 32a744ab.

CI is broken:

test/Dialect/Linalg/bufferize.mlir:274:12: error: CHECK: expected string not found in input
 // CHECK: %[[MEMREF:.*]] = tensor_to_memref %[[IN]] : memref<?xf32>
           ^