In I42fd1a130e ("Merge Lucene core and backward-codecs jars"), Dave
Borowitz introduced a script to concatenate META-INF/services/ files
for Codecs.
Buck would randomly pick one of the two service files. The solution
was to explicitly pick the first entry for class files, and
concatenate service files.
In Bazel, we can have Bazel do the work of merging jars. This is done
with the java_binary rule. This concatenates the service files, and
picks a single .class file from each input jar, as determined by the
ordering in the jars attribute.
Delete tools/merge_jars.py, as this was its only use. This also fixes
an issue where Mac users need to specify --host_force_python=PY2 if
they don't have Python 3.
Change-Id: Ibe62917e20eeb1824967782d4d510f3f63775fce
1fdd3f7b27