Remove FMODE_FASTSOCKET check in filp_close

It is unnecessary to check whether the file is fastsocket file in filp_close;
There are two kinds of file type which fastsocket could create
1. The file which is open with file "/dev/fastsocket": The mode of
this file will not be set the flag "FMODE_FASTSOCKET". And the
fsocket_release will be invoked by filp_close->fput->__fput.
2. The file which is allocated by the socket injected by fastsocket:
The socket close is also injected by fastsocket, so it will reach
fsocket_close instead of the filp_close.

To summarize, it is unnecessary to check fastsocket file in filp_close.