Convert old name "sparse compiler" to new name "sparsifier" in comments in (mlir)Sparsifier code

[TimAtGoogle]

We decided to change the original name "sparse compiler" to "sparsifier", and some of the comments are lagging behind -- rewrite all instances from the old to the new.

[llvmbot]

@llvm/issue-subscribers-mlir-sparse

Author: Tim Harvey (TimAtGoogle)

We decided to change the original name "sparse compiler" to "sparsifier", and some of the comments are lagging behind -- rewrite all instances from the old to the new.

[llvmbot]

@llvm/issue-subscribers-mlir

Author: Tim Harvey (TimAtGoogle)

We decided to change the original name "sparse compiler" to "sparsifier", and some of the comments are lagging behind -- rewrite all instances from the old to the new.