Remove orig_src_map (#4025)

**What type of PR is this?**
Code cleanup. I don't see this being used and it seems it has not been
for 6+ years.

**What does this PR do? Why is it needed?**

**Which issues(s) does this PR fix?**

Fixes #

**Other notes for review**

go/private/actions/archive.bzl

@@ -169,7 +169,6 @@ def emit_archive(go, source = None, _recompile_suffix = "", recompile_internal_d
         # GoSource fields
         srcs = as_tuple(source.srcs),
         orig_srcs = as_tuple(source.orig_srcs),
-        _orig_src_map = tuple([source.orig_src_map.get(src, src) for src in source.srcs]),
         _cover = as_tuple(source.cover),
         _embedsrcs = as_tuple(source.embedsrcs),
         _x_defs = tuple(source.x_defs.items()),

go/private/context.bzl

@@ -222,7 +222,6 @@ def _merge_embed(source, embed):
     s = get_source(embed)
     source["srcs"] = s.srcs + source["srcs"]
     source["orig_srcs"] = s.orig_srcs + source["orig_srcs"]
-    source["orig_src_map"].update(s.orig_src_map)
     source["embedsrcs"] = source["embedsrcs"] + s.embedsrcs
     source["cover"] = source["cover"] + s.cover
     source["deps"] = source["deps"] + s.deps
@@ -277,7 +276,6 @@ def _library_to_source(go, attr, library, coverage_instrumented):
         "mode": go.mode,
         "srcs": srcs,
         "orig_srcs": srcs,
-        "orig_src_map": {},
         "cover": [],
         "embedsrcs": embedsrcs,
         "x_defs": {},

go/private/rules/test.bzl

@@ -674,7 +674,6 @@ def _recompile_external_deps(go, external_source, internal_archive, library_labe
             mode = go.mode,
             srcs = as_list(arc_data.srcs),
             orig_srcs = as_list(arc_data.orig_srcs),
-            orig_src_map = dict(zip(arc_data.srcs, arc_data._orig_src_map)),
             cover = arc_data._cover,
             embedsrcs = as_list(arc_data._embedsrcs),
             x_defs = dict(arc_data._x_defs),

go/providers.rst

@@ -134,11 +134,6 @@ method. In general, only rules_go should need to build or handle these.
 | The original source files this library is based on. This may differ from                         |
 | :param:`srcs` if processing tools such as cgo or cover are applied.                              |
 +--------------------------------+-----------------------------------------------------------------+
-| :param:`orig_src_map`          | :type:`dict of File to File`                                    |
-+--------------------------------+-----------------------------------------------------------------+
-| Maps generated files in :param:`srcs` back to :param:`orig_srcs`. Not all                        |
-| generated files may appear in here.                                                              |
-+--------------------------------+-----------------------------------------------------------------+
 | :param:`embedsrcs`             | :type:`list of File`                                            |
 +--------------------------------+-----------------------------------------------------------------+
 | Files that may be embedded into the compiled package using ``//go:embed``                        |