[mlir][linalg] Remove the StructuredOp capture mechanism.

After https://reviews.llvm.org/D104109, structured ops support scalar inputs. As a result, the capture mechanism meant to pass non-shaped parameters got redundant. The patch removes the capture semantics after the FillOp migrated to use scalar operands https://reviews.llvm.org/D104121.

Differential Revision: https://reviews.llvm.org/D104785