gdb/testsuite: additional test fixes after gdb_test changes

gdb/testsuite: additional test fixes after gdb_test changes

After this commit:

  commit e2f620135d92f7cd670af4e524fffec7ac307666
  Date:   Thu Mar 30 13:26:25 2023 +0100

      gdb/testsuite: change newline patterns used in gdb_test

There were some regressions in gdb.trace/*.exp tests when run with the
native-gdbserver board.  This commit fixes these regressions.

All the problems are caused by unnecessary trailing newline characters
included in the patterns passed to gdb_test.  After the above commit
the testsuite is stricter when matching trailing newlines, and so the
additional trailing newline characters are now causing the test to
fail.  Fix by removing all the excess trailing newline characters.

In some cases this cleanup means we should use gdb_test_no_output,
I've done that where appropriate.  In a couple of other places I've
made use of multi_line to better build the expected output pattern.