travis: Use correct vorbis flag in sdl2_mixer install
Revert the addition of cmake which is already instealled.
MISC_DIR := $(call my-dir)
LOCAL_PATH := MISC_DIR
include $(MISC_DIR)/liblua/Android.mk
include $(MISC_DIR)/libphysfs/Android.mk
include $(MISC_DIR)/libphyslayer/Android.mk