manager: do not append '\n' when writing sysctl settings
    
    When booting with debug logs, we print:
    
       Setting '/proc/sys/fs/file-max' to '9223372036854775807
       '
       Setting '/proc/sys/fs/nr_open' to '2147483640
       '
       Couldn't write fs.nr_open as 2147483640, halving it.
       Setting '/proc/sys/fs/nr_open' to '1073741816
       '
       Successfully bumped fs.nr_open to 1073741816
    
    The strange formatting is because we explicitly appended a newline in those two
    places. It seems that the kernel doesn't care. In fact, we have a few dozen other
    writes to sysctl where we don't append a newline. So let's just drop those here
    too, to make the code a bit simpler and avoid strange output in the logs.
    
    (cherry picked from commit b47e0fac0356308cf34aa235ba9328c0c9de51bd)