clean up system/arc (#20792)

lib/system/arc.nim

@@ -12,26 +12,6 @@ In this new runtime we simplify the object layouts a bit: The runtime type
 information is only accessed for the objects that have it and it's always
 at offset 0 then. The ``ref`` object header is independent from the
 runtime type and only contains a reference count.
-
-Object subtyping is checked via the generated 'name'. This should have
-comparable overhead to the old pointer chasing approach but has the benefit
-that it works across DLL boundaries.
-
-The generated name is a concatenation of the object names in the hierarchy
-so that a subtype check becomes a substring check. For example::
-
-  type
-    ObjectA = object of RootObj
-    ObjectB = object of ObjectA
-
-ObjectA's ``name`` is "|ObjectA|RootObj|".
-ObjectB's ``name`` is "|ObjectB|ObjectA|RootObj|".
-
-Now to check for ``x of ObjectB`` we need to check
-for ``x.typ.name.endsWith("|ObjectB|ObjectA|RootObj|")``.
-In the actual implementation, however, we could also use a
-hash of ``package & "." & module & "." & name`` to save space.
-
 ]#
 
 when defined(gcOrc):
@@ -227,22 +207,5 @@ template tearDownForeignThreadGc* =
   ## With `--gc:arc` a nop.
   discard
 
-proc memcmp(str1, str2: cstring, n: csize_t): cint {.importc, header: "<string.h>".}
-
-func endsWith(s, suffix: cstring): bool {.inline.} =
-  let
-    sLen = s.len
-    suffixLen = suffix.len
-
-  if suffixLen <= sLen:
-    result = memcmp(cstring(addr s[sLen - suffixLen]), suffix, csize_t(suffixLen)) == 0
-
-proc isObj(obj: PNimTypeV2, subclass: cstring): bool {.compilerRtl, inl.} =
-  result = endsWith(obj.name, subclass)
-
 proc isObjDisplayCheck(source: PNimTypeV2, targetDepth: int16, token: uint32): bool {.compilerRtl, inline.} =
   result = targetDepth <= source.depth and source.display[targetDepth] == token
-
-proc chckObj(obj: PNimTypeV2, subclass: cstring) {.compilerRtl.} =
-  # checks if obj is of type subclass:
-  if not isObj(obj, subclass): sysFatal(ObjectConversionDefect, "invalid object conversion")