If it's cast iron it can be 'broken out' with a big sledge hammer and a bunch of Sweat-Equity
If it's steel/porcelein...........a reciprocating saw may do the job using the correct metal cutting blades
A gas powered cutoff saw fitted with an abrasive wheel should produce enough dust and grit to fill an entire house while cutting thru the tub........
Wear safety equipment/glasses/mask/gloves........
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