[gdb/testsuite] Clean standard_output_file dir in gdb_init

In commit e2adba909e ("[gdb/testsuite] Clean up before compilation in
gdb.ada/call-no-debug.exp") I added some code in the test-case to remove some
files at the start of the test-case:
...
remote_file host delete [standard_output_file prog.o]
remote_file host delete [standard_output_file prog.ali]
...

Replace this with cleaning up the entire directory instead, for all
test-cases.

Tested on x86_64-linux.

Suggested-By: Tom Tromey <tom@tromey.com>
Reviewed-By: Tom Tromey <tom@tromey.com>

gdb/testsuite/gdb.ada/call-no-debug.exp

@@ -21,11 +21,6 @@ require allow_ada_tests
 
 standard_ada_testfile prog
 
-# Since we use no-force to compile prog, make sure we don't pick up files
-# from a previous compilation.
-remote_file host delete [standard_output_file prog.o]
-remote_file host delete [standard_output_file prog.ali]
-
 # Compile pck without debuginfo but prog with it.
 if {[gdb_compile_ada $srcdir/$subdir/$testdir/pck.adb \
 	 [standard_output_file pck.o] object {}] != ""} {

gdb/testsuite/lib/gdb.exp

@@ -6420,6 +6420,9 @@ proc default_gdb_init { test_file_name } {
 
     set gdb_test_file_name [file rootname [file tail $test_file_name]]
 
+    # Clean directory containing the standard output files.
+    remote_exec build "rm -rf [standard_output_file ""]"
+
     # Make sure that the wrapper is rebuilt
     # with the appropriate multilib option.
     if { $gdb_wrapper_target != [current_target_name] } {