Assorted synth fixups / cleanups (#6400)
Assorted synth fixups / cleanups (#6400)

* Asset: Replace 'stable' -> 'latest' in docs links, caused by out-of-date synth.
* AutoML: fix copying generated docs.
* Bigtable: remove now-spurious fixup from 'synth.py'.
* DLP: remove now-spurious fixups from 'synth.py'.
* Monitoring: remove now-spurious fixups from 'synth.py'.
* Redis: remove now-spurious fixups from 'synth.py'.
* Speech: remove now-spurious fixups from 'synth.py'.
googleapis/python-automl,googleapis/python-automl