Remove a few instances where we look up a command by name, but could
just use the return value of a previous "add command" function call
instead.
gdb/ChangeLog:
* mi/mi-main.c (_initialize_mi_main):
* python/py-auto-load.c (gdbpy_initialize_auto_load):
* remote.c (_initialize_remote):
Change-Id: I6d06f9ca636e340c88c1064ae870483ad392607d