Since 24dd6740 UpdateCheckMode: Tags uses the found tag instead of
regenerating it from the AutoUpdateMode pattern making the pattern
superfluous. This adds support for dropping the pattern and a test case.
The .txt format was the last place where the lowercase "builds" was used,
this converts references everywhere to be "Builds". This makes it possible
to load metadata YAML files with any YAML parser, then have it possible to
use fdroidserver methods on that data, like metadata.write_metadata().
The test files in tests/metadata/dump/*.yaml were manually edited by cutting
the builds: block and putting it the sort order for Builds: so the contents
should be unchanged.
```
sed -i \
-e 's/app\.builds/app.get('Builds', \[\])/g' \
-e "s/app\.get(Builds, \[\]) =/app\['Builds'] =/g" \
-e "s/app\.get(Builds, \[\]) =/app\['Builds'] =/g" \
-e "s/app\.get(Builds, \[\])/app.get('Builds', \[\])/g" \
-e "s/app\.get('Builds', \[\])\.append/app\['Builds'\].append/g" \
-e "s/app\['builds'\]/app.get('Builds', [])/g" \
*/*.*
```
