Be careful, not every song is going to have correct grammar.
However, there really is no place for the word "is" in these lyrics.
"Sick of policies leaving me out"
So, the singer IS sick of policies leaving him out.
But, this is in the first person form, so the singer is speaking of himself in this line.
So this line: "Sick of policies leaving me out"
Means: "I am sick of policies leaving me out"
There is no place for "is" to function as a linking verb in this sentence, so it is not needed.