BSD.usr.dist: remove obsolete usr/share/examples/drivers entry

In base 8f0a6a9aad, usr/share/examples/drivers was cleaned up,
because it contained unmaintained scripts. The directory itself is
cleaned up by ObsoleteFiles.inc, but there was still an entry in
BSD.usr.dist that re-created the directory. Remove it.

Fixes:		8f0a6a9aad
MFC after:	3 days

(cherry picked from commit ac2f284258)

etc/mtree/BSD.usr.dist

@@ -260,8 +260,6 @@
             ..
             dma
             ..
-            drivers
-            ..
             dwatch
             ..
             etc