Use gflags with bazel the way it recommends

Also lets us remove the hand-generated headers which are now out of
date.

Change-Id: I8673300b6c8c4e7a32e68a07d48ac79cb59faa62
diff --git a/y2018/control_loops/superstructure/arm/BUILD b/y2018/control_loops/superstructure/arm/BUILD
index bf30121..e8af2b9 100644
--- a/y2018/control_loops/superstructure/arm/BUILD
+++ b/y2018/control_loops/superstructure/arm/BUILD
@@ -43,7 +43,7 @@
     deps = [
         "//frc971/control_loops:runge_kutta",
         "//third_party/eigen",
-        "//third_party/gflags",
+        "@com_github_gflags_gflags//:gflags",
     ],
 )
 
@@ -78,8 +78,8 @@
         ":generated_graph",
         ":trajectory",
         "//third_party/eigen",
-        "//third_party/gflags",
         "//third_party/matplotlib-cpp",
+        "@com_github_gflags_gflags//:gflags",
     ],
 )