TAKE - yet more pagebuf code rationalization

[Steve Lord <lord@sgi.com>]

Some more code removal - left behind from previous simplifications,
remove some locking from the read path.

Date:  Tue Apr  3 09:22:18 PDT 2001
Workarea:  jen.americas.sgi.com:/src/lord/xfs-linux.2.4

The following file(s) were checked into:
  bonnie.engr.sgi.com:/isms/slinx/2.4.x-xfs


Modid:  2.4.x-xfs:slinx:91469a
linux/fs/xfs/linux/xfs_lrw.c - 1.87
	- Less locking in the read path, cleanup lock mode calculation in the write
	  path and remove the PBMF_NEW flag.

linux/include/linux/page_buf.h - 1.84
	- Remove some dead definitions.

linux/fs/pagebuf/page_buf.c - 1.71
	- Simplify some more code, removing dead paths and unused calculations
	  left over from previous versions of the code.

linux/fs/pagebuf/page_buf_io.c - 1.73
	- Remove some dead code, optimize out the prepare_write call when the page
	  is already upto date, deal with EAGAIN coming back from the strategy call.