Remove slf4j-api reference in LICENSE (#12052)

[Fokko]

Work by @jbonofre, let's include this in 1.7.2 as well:

I've checked out the branch, and it is also excluded from the JAR on the 1.7.x branch:

➜  azure find . | grep -i slf4j
./org/apache/iceberg/azure/shaded/io/netty/util/internal/logging/LocationAwareSlf4JLogger.class
./org/apache/iceberg/azure/shaded/io/netty/util/internal/logging/Slf4JLoggerFactory$NopInstanceHolder.class
./org/apache/iceberg/azure/shaded/io/netty/util/internal/logging/Slf4JLoggerFactory.class
./org/apache/iceberg/azure/shaded/io/netty/util/internal/logging/Slf4JLogger.class
./reactor/util/Loggers$Slf4JLoggerFactory.class
./reactor/util/Loggers$Slf4JLogger.class

➜  gcp find . | grep -i slf4j                                                                               
./io/grpc/netty/shaded/io/netty/util/internal/logging/LocationAwareSlf4JLogger.class
./io/grpc/netty/shaded/io/netty/util/internal/logging/Slf4JLoggerFactory$NopInstanceHolder.class
./io/grpc/netty/shaded/io/netty/util/internal/logging/Slf4JLoggerFactory.class
./io/grpc/netty/shaded/io/netty/util/internal/logging/Slf4JLogger.class

➜  aws find . | grep -i slf4j                     
./org/apache/iceberg/aws/shaded/io/netty/util/internal/logging/LocationAwareSlf4JLogger.class
./org/apache/iceberg/aws/shaded/io/netty/util/internal/logging/Slf4JLoggerFactory$NopInstanceHolder.class
./org/apache/iceberg/aws/shaded/io/netty/util/internal/logging/Slf4JLoggerFactory.class
./org/apache/iceberg/aws/shaded/io/netty/util/internal/logging/Slf4JLogger.class

[jbonofre]

Thanks @Fokko !