remove backtrace (now part of vendor)

preparing to do a full rewrite of the prototype (curation of old code)

code/sectr/grime/pkg_mappings.odin

@@ -163,11 +163,6 @@ import "core:unicode/utf8"
 
 //endregion core
 
-import "thirdparty:backtrace"
-	StackTraceData   :: backtrace.Trace_Const
-	stacktrace       :: backtrace.trace
-	stacktrace_lines :: backtrace.lines
-
 //region codebase
 
 import "codebase:grime"