Change to use single definition of "PI"

BUG=aomedia:1943

Change-Id: Ia70b8e4fb5e67270caa3748e9bb5e821d439b51a

aom_dsp/add_noise.c

diff --git a/aom_dsp/add_noise.c b/aom_dsp/add_noise.c
index bfb3e7e..43587ca 100644
--- a/aom_dsp/add_noise.c
+++ b/aom_dsp/add_noise.c
@@ -40,7 +40,7 @@
 }
 
 static double gaussian(double sigma, double mu, double x) {
-  return 1 / (sigma * sqrt(2.0 * 3.14159265)) *
+  return 1 / (sigma * sqrt(2.0 * PI)) *
          (exp(-(x - mu) * (x - mu) / (2 * sigma * sigma)));
 }
 

tools/txfm_analyzer/txfm_graph.h

diff --git a/tools/txfm_analyzer/txfm_graph.h b/tools/txfm_analyzer/txfm_graph.h
index 2e3c955..8dc3614 100644
--- a/tools/txfm_analyzer/txfm_graph.h
+++ b/tools/txfm_analyzer/txfm_graph.h
@@ -23,7 +23,6 @@
   int visited;
 };
 
-#define PI (3.141592653589793238462643383279502884)
 #define STAGENUM (10)
 #define NODENUM (32)
 #define COS_MOD (128)