[mlir][linalg][bufferize][NFC] Remove RewriterBase from BufferizationState

This change simplifies BufferizationState. Having `rewriter` in BufferizationState could be confusing to users because a rewriter is also passed to each `bufferize` function and it is not obvious (by looking at the API) that these two rewriters are the same.

Differential Revision: https://reviews.llvm.org/D116444