[gdb/testsuite, tclint] Fix gdb.server

Running tclint on the test-cases in gdb.server shows a few problems:
...
connect-with-no-symbol-file.exp:72:1: line has trailing whitespace \
  [trailing-whitespace]
exit-multiple-threads.exp:73:5: expected braced word or word without \
substitutions in argument interpreted as expr [command-args]
extended-remote-restart.exp:73:5: expected braced word or word without \
  substitutions in argument interpreted as expr [command-args]
monitor-exit-quit.exp:73:5: expected braced word or word without \
  substitutions in argument interpreted as expr [command-args]
reconnect-ctrl-c.exp:54:5: expected braced word or word without \
  substitutions in argument interpreted as expr [command-args]
server-exec-info.exp:24:1: expected braced word or word without \
  substitutions in argument interpreted as expr [command-args]
stop-reply-no-thread.exp:73:5: expected braced word or word without \
  substitutions in argument interpreted as expr [command-args]
/stop-reply-no-thread-multi.exp:81:5: expected braced word or word without \
  substitutions in argument interpreted as expr [command-args]
...

Fix these.

Tested on aarch64-linux.