gdb/testsuite: Remove duplicates from gdb.mi/mi-language.exp

gdb/testsuite: Remove duplicates from gdb.mi/mi-language.exp

When running the testsuite, I have:

    Running .../gdb/testsuite/gdb.mi/mi-language.exp ...
    DUPLICATE: gdb.mi/mi-language.exp: set lang ada

This is due to an erroneous explicit test name.  This explicit test name
also happens to be useless (at least it would have been if it was
correct) since it only repeats the command, so just remove the explicit
test name and let the command be used as default test name.  Also remove
explicit test name at another location in the file since it also just
repeat the command.

Tested on x86_64-linux.