do not create shebang.bak file

lib/spack/spack/hooks/sbang.py

@@ -34,6 +34,7 @@
 # here, as it is the shortest I could find on a modern OS.
 shebang_limit = 127
 
+
 def shebang_too_long(path):
     """Detects whether a file has a shebang line that is too long."""
     with open(path, 'r') as script:
@@ -57,16 +58,10 @@ def filter_shebang(path):
     if original.startswith(new_sbang_line):
         return
 
-    backup = path + ".shebang.bak"
-    os.rename(path, backup)
-
     with open(path, 'w') as new_file:
         new_file.write(new_sbang_line)
         new_file.write(original)
 
-    copy_mode(backup, path)
-    unset_executable_mode(backup)
-
     tty.warn("Patched overly long shebang in %s" % path)