dropped relics of ancient side-entry points

--- a/src/HOL/base.ML	Mon Dec 31 21:41:22 2012 +0100
+++ /dev/null	Thu Jan 01 00:00:00 1970 +0000
@@ -1,4 +0,0 @@
-
-(* side-entry for HOL-Base *)
-
-use_thys ["HOL"];

--- a/src/HOL/main.ML	Mon Dec 31 21:41:22 2012 +0100
+++ /dev/null	Thu Jan 01 00:00:00 1970 +0000
@@ -1,4 +0,0 @@
-
-(* side-entry for HOL-Main *)
-
-use_thys ["Main"];

--- a/src/HOL/plain.ML	Mon Dec 31 21:41:22 2012 +0100
+++ /dev/null	Thu Jan 01 00:00:00 1970 +0000
@@ -1,4 +0,0 @@
-
-(* side-entry for HOL-Plain *)
-
-use_thys ["Plain"];