Don't load from @// in the main repository

It's unusual and unnecessary.

Change-Id: Id0e51eaeb492cd8444d4caf53c35edf43c45223c
diff --git a/third_party/BUILD b/third_party/BUILD
index 1ef7169..8bd83d7 100644
--- a/third_party/BUILD
+++ b/third_party/BUILD
@@ -1,4 +1,4 @@
-load("@//tools/build_rules:select.bzl", "cpu_select")
+load("//tools/build_rules:select.bzl", "cpu_select")
 
 cc_library(
     name = "wpilib",