Rename 'extdir' to 'extclasspath'

The targets contain the entries in the extdir and are used to
construct a classpath, so the label is not actually a directory.

--
PiperOrigin-RevId: 147798672
MOS_MIGRATED_REVID=147798672
diff --git a/tools/jdk/BUILD b/tools/jdk/BUILD
index b717f9f..0bd8db3 100644
--- a/tools/jdk/BUILD
+++ b/tools/jdk/BUILD
@@ -77,7 +77,7 @@
 )
 
 alias(
-    name = "extdir",
+    name = "extclasspath",
     actual = "@local_jdk//:extdir",
 )
 
@@ -106,7 +106,7 @@
     name = "toolchain",
     bootclasspath = [":bootclasspath"],
     encoding = "UTF-8",
-    extclasspath = [":extdir"],
+    extclasspath = [":extclasspath"],
     forcibly_disable_header_compilation = 0,
     genclass = ["//tools/jdk:GenClass_deploy.jar"],
     header_compiler = ["//tools/jdk:turbine_deploy.jar"],