Remove ineffective argument from sample

[jansauer]

Based on the documentation of the individual env vars, OVERPASS_META only applies on init mode. Since this docker run example is using the clone mode the OVERPASS_META is ineffective and only makes the sample more complex and confusing.

[wiktorn]

OVERPASS_META argument is also used when running update scripts as well as starting dispatcher. I'm not sure, if removing it will not affect the functionality. I do not have necessary infrastructure to test cloned instance.

[jansauer]

Oh, I forgot to think about the update the script.

Overpass-API/README.md

Line 8 in b40e832

* `OVERPASS_META` - (`init` mode only) `yes`, `no` or `attic` - passed to Overpass as `--meta` or `--keep-attic`.

Based on the init mode only line i thought that setting this env var in mode clone does not have any effect. Since I'm running my instance in clone mode and without this setting I will try to understand if this results in any problems for my instance.

@wiktorn thx for the feedback.