Remove linux_memcheck from default trybots.
Remove linux_memcheck from default trybots.

Now that we have enabled leak detection (LeakSanitizer) for our
Linux ASan bots, there's no point always running the linux_memcheck trybot
since it's very slow and almost always gets a long queue of builds.

BUG=
R=niklas.enbom@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/28479004

git-svn-id: 917f5d3ca488f358c4d40eaec14422cf392ccec9@7203 4adac7df-926f-26a2-2b94-8c16560cd09d

mwgoldsmith/ilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,mwgoldsmith/ilbc,mwgoldsmith/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,mwgoldsmith/ilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,mwgoldsmith/libilbc,TimothyGu/libilbc,mwgoldsmith/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,mwgoldsmith/ilbc,mwgoldsmith/libilbc