Well, it depends on what you mean by "life support" because strictly speaking, ANYTHING that is artificial that supports life can be considered "life support." This then will include a feeding tube.
To avoid confusion, I used the term "artificial treatment" since humans weren't able to keep people alive by implanting a tube directly into a patient's stomach before the past few decades.
The law of Florida counts this as life support. And yes, we couldn't implant tubes before the last half of the last century.
There was no reason to remove the tube other than in anticipation of Felos' argument that it would be cruel to reinsert it.
In the meantime, Schiavo - not Terri's doctor - has forbidden sips of water, ice chips or anything by mouth.
The intention is to cause death, not to allow death. If the wish were to "let her go" Michael would allow oral hydration.
As her body starves, it will break down fat, resulting in ketosis, acidic blood. She will hyperventilate as long as she has the strength, in order to blow off carbon dioxide to get rid of the acid. She will make increased urine until her kidneys fail in another attempt to get rid of the acid in the form of ketones.
The dehydration will be uncomfortable and exhausting. Unless she is sedated somehow. The sedation will prevent the hyperventilation, speeding death due to acidosis.