sys/targets: use kernel.full instead of kernel.debug
sys/targets: use kernel.full instead of kernel.debug

The latter contains only debug symbols and is meant to be used with the
kernel executable.  That is, the kernel executable contains a
.gnu_debuglink pointer to kernel.debug.  kernel.full contains
everything, including a copy of the kernel's text section, which we want
when enumerating __sanitizer_cov_trace_pc() calls for a coverage report.

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