gdb/testsuite: use proc_with_prefix in gdb.guile/scm-breakpoint.exp

Convert gdb.guile/scm-breakpoint.exp to use proc_with_prefix instead
of using nested with_test_prefix calls.  Allows a level of indentation
to be removed from most of the test procs.

There were two procs that didn't use with_test_prefix, but I converted
them to be proc_with_prefix anyway, for consistency.

gdb/testsuite/ChangeLog:

	* gdb.guile/scm-breakpoint.exp (test_bkpt_basic): Convert to
	'proc_with_prefix', remove use of 'with_test_prefix', and
	reindent.
	(test_bkpt_deletion): Likewise.
	(test_bkpt_cond_and_cmds): Likewise.
	(test_bkpt_invisible): Likewise.
	(test_watchpoints): Likewise.
	(test_bkpt_internal): Likewise.
	(test_bkpt_eval_funcs): Likewise.
	(test_bkpt_registration): Likewise.
	(test_bkpt_address): Convert to 'proc_with_prefix'.
	(test_bkpt_probe): Likewise.