[FLINK-898] Clean up distribution default config

This PR cleans up the distribution default config.

Removed entries:
- `env.java.home`,
- `env.java.opts`,
- `jobmanager.profiling.enable`,
- `jobmanager.rpc.handler`, 
- `jobmanager.web.history`,
- `taskmanager.rpc.port`,
- `taskmanager.network.bufferSizeInBytes`,
- `webclient.rootpath`,
- `webclient.tempdir`,
- `webclient.uploaddir`, and
- `webclient.plandump`.

Active entries:
- `jobmanager.rpc.address: localhost`
- `jobmanager.rpc.port: 6123`,
- `jobmanager.heap.mb: 256`,
- `taskmanager.heap.mb: 512`,
- `parallelization.degree.default: 1`,
- `jobmanager.web.port: 8081`, and
- `webclient.port: 8080`.

Suggested entries:
- `taskmanager.network.numberOfBuffers: 2048`,
- `taskmanager.tmp.dirs: /tmp`, and
- `fs.hdfs.hadoopconf: /path/to/hadoop/conf/`.

`webclient.port` and `taskmanager.network.numberOfBuffers` will be removed in the future, when the web interfaces have been merged and the memory management reworked.