Configure vp10 disabled by default

To turn on vp10, one needs to explicitly set --enable-vp10.

Change-Id: Ifc7e294aea9a5bdf5d08f0001ae26fba5a837b64

configure

diff --git a/configure b/configure
index 3ecb2ce..ac196da 100755
--- a/configure
+++ b/configure
@@ -194,6 +194,9 @@
 [ -d "${source_path}/vp9" ] || disable_feature vp9
 [ -d "${source_path}/vp10" ] || disable_feature vp10
 
+# disable vp10 codec by default
+disable_feature vp10
+
 # install everything except the sources, by default. sources will have
 # to be enabled when doing dist builds, since that's no longer a common
 # case.