travis/prepare.sh: don't set XBPS_{PKG,REPO}_COMPTYPE.

Use xbps defaults.

common/travis/prepare.sh

@@ -10,8 +10,6 @@ echo XBPS_ALLOW_RESTRICTED=yes >> etc/conf
 /bin/echo -e '\x1b[32mEnabling ethereal chroot-style...\x1b[0m'
 echo XBPS_CHROOT_CMD=ethereal >> etc/conf
 echo XBPS_ALLOW_CHROOT_BREAKOUT=yes >> etc/conf
-echo XBPS_PKG_COMPTYPE=lz4 >> etc/conf
-echo XBPS_REPO_COMPTYPE=lz4 >> etc/conf
 
 /bin/echo -e '\x1b[32mLinking / to /masterdir...\x1b[0m'
 ln -s / masterdir