You could do this in R, using seqinR:

library(seqinr)
x=read.fasta("yourfile.fasta")
write.fasta(x,file="newfile.fasta",names=names(x))

How about this (untested):

#!/usr/bin/env python
import sys
from Bio import SeqIO

fasta_file = sys.argv[1]  # Input fasta file
result_file = sys.argv[2] # Output fasta file

def modified(records):
    for record in records:
        #Clear the description
        record.description=""
        yield record

records = modified(SeqIO.parse(fasta_file),"fasta")
count = SeqIO.write(records, result_file, "fasta")
print "Converted %i records" % count

This used a generator function to modify the records (memory efficient - you should avoid loading everything into memory). The key point for your request was to set the description to an empty string.