linker: remove link from external library on unload

When unloading library make sure the soinfo_link to parent
from linked external libraries is removed as well.

FPIIM-1135
FPIIM-1126

Bug: 36104177
Bug: http://b/37433850
Test: manual
Merged-In: I601b54144acecac54744805b38313c46045c54cb
Change-Id: I601b54144acecac54744805b38313c46045c54cb
(cherry picked from commit 6fa537f8cbfc9aa48e322e8080e56a408c158292)
diff --git a/linker/linked_list.h b/linker/linked_list.h
index 8003dbf..0572e63 100644
--- a/linker/linked_list.h
+++ b/linker/linked_list.h
@@ -127,7 +127,13 @@
         } else {
           p->next = next;
         }
+
+        if (tail_ == e) {
+          tail_ = p;
+        }
+
         Allocator::free(e);
+
         e = next;
       } else {
         p = e;