port api/send.py to Python 3

[HrachShah]

Summary

api/send.py still uses three Python 2 idioms that prevent the file from being imported on Python 3 (and therefore prevent the entire WSGI app from starting, since msc_apps.py imports this module transitively):

1. import urlparse — the module was renamed to urllib.parse in Python 3. Raises ModuleNotFoundError: No module named 'urlparse' at import time. The module is never referenced in this file (only urlparse.parse_qs is used in msc_apps.py, which is a separate module already covered by an earlier PR), so the line is just removed.
2. response_dict.has_key(field) — .has_key() was removed from dicts in Python 3 (use in instead). Two call sites.
3. Six print statements without parentheses — Python 3 only supports the function form.

This is the same Python 2 → 3 migration that earlier sessions applied to armory_service.py, pending.py, msc_apps.py, rpcclient.py, and pushtx.py in the api package.

Verification

ast.parse() on the patched file succeeds. No remaining Python 2 patterns (import urlparse, has_key, unparenthesized print) in the file. Behavior is unchanged for the Python 2 call sites (the in operator matches .has_key() semantics, the print function matches the Python 2 print statement semantics for the simple cases used here).