Stop a tramp test leaving a file behind

* test/lisp/net/tramp-tests.el
(tramp-test10-write-region-file-precious-flag):
Avoid leaving a backup file after we are done.
1 job for master in 54 minutes and 43 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Test
failed #2164
test-all

00:54:43

 
Name Stage Failure
failed
test-all Test
Makefile:318: recipe for target 'check-doit' failed
make[2]: *** [check-doit] Error 1
make[2]: Leaving directory '/builds/emacs/emacs/test'
Makefile:293: recipe for target 'check-expensive' failed
make[1]: *** [check-expensive] Error 2
make[1]: Leaving directory '/builds/emacs/emacs/test'
Makefile:957: recipe for target 'check-expensive' failed
make: *** [check-expensive] Error 2
ERROR: Job failed: exit code 1