lapack_testing.py: remove nonexistent flag in doc

The `-x` flag was never a valid short option for the `getopt` command
line parser.

Author: christoph-conrads

lapack_testing.py

@@ -35,7 +35,6 @@
         print("     - d [dir] is to indicate where is the LAPACK testing directory (.out files). By default, the script will use .")
         print("     - b [bin] is to indicate where is the LAPACK binary files are located. By default, the script will use .")
         print(" LEVEL OF OUTPUT")
-        print("     - x is to print a detailed summary")
         print("     - e is to print only the error summary")
         print("     - s is to print a short summary")
         print("     - n is to print the numbers of failing tests (turn on summary mode)")