If you are using the Fabric MoPub integration, there currently is not a way to disable these logs as Fabric is not open source.
If you are using the MoPub SDK integration, please follow the below steps.
In the file MPLogging.m, change the line
static MPLogLevel systemLogLevel = MPLogLevelInfo;
to:
static MPLogLevel systemLogLevel = MPLogLevelOff;
Please see the below on references to log levels: