Why pluto is removed from planet?

Pluto was ruled not a planet anymore because it is a "dwarf  planet"

Apparently, the International Astronomical Union's (IAU) definition of a planet includes that a planet should be part of a body that would orbit the sun.  

According to the IAU, there are three criteria's that contribute to a planet being called a planet.

1. It is within orbit around the Sun.

2. It has a sufficient mass to assume a nearly round shape

and 3. It has "cleared the neighborhood" around it's orbit.

Pluto only so happens to meet 2 of these requirements, not including the third option.

In august 2006 the international astronomical union (IAU) downgraded the status of Pluto to that of "Dwarf planet." this means that from now on only the rocky worlds of the inner solar system and the gas giants of the outer system will be designated.

("Hope this is helpful.")