Get rid of XLogCtlInsert->forcePageWrites
After commit
39969e2a1e4d, ->forcePageWrites is no longer very
interesting: we can just test whether runningBackups is different from 0.
This simplifies some code, so do away with it.
Reviewed-by: Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>
Discussion: https://postgr.es/m/
39969e2a1e4d7f5a37f3ef37d53bbfe171e7d77a