util: Get rid of virFileFlock()

util: Get rid of virFileFlock()

It was created to get rid of conditional compilation in the resctrl code and
make it usable anywhere else.  However this is not something that is going to be
used in other places because it is not portable and resctrl is just very
specific in this regard.  And there is no reason why there could not be a
preprocessor conditional in the resctrl code.  Also the interface of
virFileFlock() was very ambiguous which lead to some issues.

Signed-off-by: Martin Kletzander <mkletzan@redhat.com>
Reviewed-by: Andrea Bolognani <abologna@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>