find libzstd from the system libraries on Ubuntu

Summary:
On Ubuntu systems libzstd-dev is available through `apt-get`, so change
`getdeps.py` to install it that way rather than building it from a clone of
the github repository.  Building it locally produces some build warnings for
other projects that use `zstd` if they can find it both via `external/install`
and via the system library paths.

Reviewed By: chadaustin

Differential Revision: D10503907

fbshipit-source-id: 93129c39a9ee21f835ff9a87d9569b496324ec43

getdeps.py

@@ -204,12 +204,6 @@ def get_projects(opts):
             GitUpdater("https://github.com/skystrife/cpptoml.git"),
             CMakeBuilder(),
         ),
-        Project(
-            "zstd",
-            opts,
-            GitUpdater("https://github.com/facebook/zstd.git"),
-            MakeBuilder(),
-        ),
         Project(
             "rocksdb",
             opts,
@@ -308,7 +302,7 @@ def install_platform_deps():
             "libevent-dev flex bison libgoogle-glog-dev libkrb5-dev "
             "libsnappy-dev libsasl2-dev libnuma-dev libcurl4-gnutls-dev "
             "libpcap-dev libdb5.3-dev cmake libfuse-dev libgit2-dev mercurial "
-            "libsqlite3-dev "
+            "libsqlite3-dev libzstd-dev"
         ).split()
         install_apt(ubuntu_pkgs)
     else: