Remove references to beta domain

[eyeseast]

Examples:

BETA_ID_CUTOFF              = 20000000,
BETA_OEMBED_RESOURCE_DOMAIN = 'beta.documentcloud.org',
BETA_OEMBED_DOMAIN_MATCH    = '#https?://(www\.)?(beta|embed).documentcloud.org/.*#i',
BETA_OEMBED_PROVIDER        = 'https://api.beta.documentcloud.org/api/oembed';

Everything has been on api.www for a few years now.