Remove --swig-executable `which swig` from Xcode prepare_bindings.py call.
Remove --swig-executable `which swig` from Xcode prepare_bindings.py call.

This is no longer needed with --find-swig, and although innocuous on systems with
swig in the path, it blows up when there is no swig in the path.  This should
have been removed in the prior check-in.


git-svn-id: 4c4cc70b1ef44ba2b7963015e681894188cea27e@253353 91177308-0d34-0410-b5e6-96231b3b80d8

apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb