Use boards/local-board.exp more

Use boards/local-board.exp more

local-board.exp was introduced recently, containing the code required to
force the gdbserver boards to be non-remote (from the DejaGNU point of
view).  Other board files use the same trick of forcing isremote to 0.
Instead of doing it by hand in each file, include local-board.exp.

gdb/testsuite/ChangeLog:

	* boards/cc-with-tweaks.exp: Include local-board.exp instead of
	setting isremote by hand.
	* boards/dwarf4-gdb-index.exp: Likewise.
	* boards/fission.exp: Likewise.
	* boards/stabs.exp: Likewise.