Revert "[AMDGPU] Enable scheduler mfma rewrite stage by default" (#185604)
Reverts llvm/llvm-project#180751
Enabling this pass by default breaks a few tests / use cases downstream.
@frederik-h was also looking into the actual implementation of the pass.
For now: Just revert that pass to be on-by-default.
Also fix a typo in the process.
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Co-authored-by: Jay Foad <jay.foad@amd.com>