Revert "Enable ALT_INTRA experiment by default."

This reverts commit 8e55c2ebc7a6aed53b0b25376a83a73cfcf55943.

This change causes unit tests to fail (test_intra_pred_speed)
/ crash (x86-linux-gcc) with no experiments enabled.

BUG=aomedia:384

Change-Id: I5c8c51a9fe33287c2a4d8b9985ca97388b8790c8

configure

diff --git a/configure b/configure
index df9c290..fa3a0bc 100755
--- a/configure
+++ b/configure
@@ -475,7 +475,6 @@
     ! enabled ans && soft_enable daala_ec
     soft_enable ec_multisymbol
     soft_enable palette
-    soft_enable alt_intra
 
     # Fix up experiment dependencies
     enabled pvq && enable_feature ec_adapt