ref_tracker: remove redundant __GFP_NOWARN

Commit 16f5dfbc ("gfp: include __GFP_NOWARN in GFP_NOWAIT") made
GFP_NOWAIT implicitly include __GFP_NOWARN.

Therefore, explicit __GFP_NOWARN combined with GFP_NOWAIT (e.g.,
`GFP_NOWAIT | __GFP_NOWARN`) is now redundant.  Let's clean up these
redundant flags across subsystems.

No functional changes.

Link: https://lkml.kernel.org/r/20250805023031.331718-1-rongqianfeng@vivo.com


Signed-off-by: Qianfeng Rong <rongqianfeng@vivo.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>