* gdb.base/break-interp.exp: Remove $exec.debug safety removal.
* gdb.base/sepdebug.exp: Remove .debug subdirectory handling. New
variable different_dir. Move debugfile into a full directory pathname
under DIFFERENT_DIR.
* lib/gdb.exp (separate_debug_filename): Remove.
(gdb_gnu_strip_debug): No longer call separate_debug_filename. Remove
variable debug_dir and mkdir of it. Update function comments.