Fix for 140-char replies being unexpectedly cropped when bridged to Twitter.

Fix for 140-char replies being unexpectedly cropped when bridged to Twitter.

This drops the '@' -> ' @' hack for CURL meta-chars in outgoing Twitter bridge, added in commit 04b95c25 back in the day.
The Twitter bridge has since been switched from using direct CURL calls to using HTTPClient, which even with the CURL backend enabled doesn't trigger this issue, as POST parameters are formatted directly.
Prepending the space before we did the message cropping was leading to 140-char messages getting cropped unnecessarily, which was confusing:

Examples of broken messages:
http://identi.ca/notice/57172587 vs http://twitter.com/marjoleink/status/28398050691
http://identi.ca/notice/57172878 vs http://twitter.com/marjoleink/status/28398492563