Switch commoncpp2 to ucommon to solve dependency conflicts.

libccrtp was depending on commoncpp2, and have been replaced by a version
depending on ucommon as well.
diff --git a/jni/libzrtp/sources/bnlib/ec/ecdh.c b/jni/libzrtp/sources/bnlib/ec/ecdh.c
index 8d1bc23..25ea8cd 100644
--- a/jni/libzrtp/sources/bnlib/ec/ecdh.c
+++ b/jni/libzrtp/sources/bnlib/ec/ecdh.c
@@ -9,7 +9,7 @@
 #include <ec/ec.h>
 #include <ec/ecdh.h>
 
-int ecdhGeneratePublic(const EcCurve *curve, EcPoint *Q, const BigNum *d)
+int ecdhGeneratePublic(const NistECpCurve *curve, EcPoint *Q, const BigNum *d)
 {
     EcPoint G;
 
@@ -21,10 +21,10 @@
 
     FREE_EC_POINT(&G);
 
-    return ecCheckPubKey(curve, Q);
+    return 0;
 }
 
-int ecdhComputeAgreement(const EcCurve *curve, BigNum *agreement, const EcPoint *Q, const BigNum *d)
+int ecdhComputeAgreement(const NistECpCurve *curve, BigNum *agreement, const EcPoint *Q, const BigNum *d)
 {
     EcPoint t0;