Remove obsolete `-i` parameter from shebang

[mkhl]

The -i flag is obsolete and generates the following error:

error: the flag '-i' is no longer required and has been removed; use 'swift input-filename'

[infininight]

Simplified in https://github.com/textmate/swift.tmbundle/commit/a9ff3cd1fce663cdd8d1ce689d396b2bc891f453 which also removes the env snippet in favor of the Shell Script bundle snippet.