This keeps the Long Term Support release and the latest release installed.
r10e was kept in because it needs a special extraction method, since it is
a .bin file, not a .zip.  r12b is kept in because it is the old default.
Here is a survey of the NDK versions used in the most recent Builds entry
in each app that uses the NDK:

{'r10e': 6,
 'r12b': 93,
 'r13b': 4,
 'r14b': 5,
 'r15c': 7,
 'r16b': 14,
 'r17b': 4,
 'r17c': 7,
 'r18b': 9,
 'r19c': 17,
 'r20': 1,
 'r20b': 22,
 'r21': 3,
 'r21d': 56,
 'r21e': 65,
 'r22': 9,
 'r22b': 15,
 'r9b': 1}

#517


import glob
import os
import yaml

try:
    from yaml import CSafeLoader as SafeLoader
except ImportError:
    from yaml import SafeLoader

ndks = dict()
for f in glob.glob('metadata/*.yml'):
    with open(f) as fp:
        app = yaml.load(fp, Loader=SafeLoader)
        if app.get('Disable'):
            continue
        build = app.get('Builds', [])[-1]
        if build.get('disabled'):
            continue
        ndk = build.get('ndk')
        if ndk and ndk[1] == '9':
            print(f, build)
        elif ndk and int(ndk[2:3]) < 18:
            print(f, build)
        if ndk:
            print(f, ndk)
            if ndk not in ndks:
                ndks[ndk] = 0
            ndks[ndk] += 1

import pprint

pprint.pprint(ndks)