Delve compiles the debuggee to __debug_bin in the session's cwd (on
Windows __debug_bin.exe plus __debug_bin.exe<digits> in DAP mode) and
removes it on a graceful exit. When shutdown doesn't reach that cleanup
the binaries pile up in the project directory.
After the session is down — the adapter disconnected and its process
reaped — remove the leftover files matching Delve's own names from the
session's cwd. Only a locally started adapter (no debugServer) is swept:
a remote Delve's cwd may be on another machine. Files that merely share
the prefix (__debug_bin.go sources, in-progress names with other
suffixes, directories) are left alone.
Fixes#1790