g++: Rely on dg-do-what-default to avoid running pr102788.cc on non-vector targets

g++: Rely on dg-do-what-default to avoid running pr102788.cc on non-vector targets

Testcases in g++.dg/vect rely on check_vect_support_and_set_flags
to set dg-do-what-default and avoid running vector tests on non-vector
targets. The testcase in this patch overwrites the default with
dg-do run.

Removing the dg-do run directive resolves this issue for non-vector
targets (while still running the tests on vector targets).

gcc/testsuite/ChangeLog:

	* g++.dg/vect/pr102788.cc: Remove dg-do run directive.

Signed-off-by: Patrick O'Neill <patrick@rivosinc.com>