Removed some unused imports.

src/node.py

@@ -10,8 +10,6 @@ from graph_drawing.graph import generate_graph
 from graph_drawing.line import generate_line
 from graph_drawing.node import Node, Leaf
 
-from unicode_math import PI as u_PI
-
 
 TYPE_OPERATOR = 1
 TYPE_IDENTIFIER = 2

src/rules/integrals.py

-from .utils import find_variables, infinity, replace_variable, find_variable, \
-        absolute
+from .utils import find_variables, replace_variable, find_variable, absolute
 from .logarithmic import ln
 from .goniometry import sin, cos
 from ..node import ExpressionNode as N, ExpressionLeaf as L, OP_INT, \