rename nimEnableHashRef [backport] (#18941)

* rename nimEnableHashRef [backport]
* Apply suggestions from code review

Co-authored-by: konsumlamm <44230978+konsumlamm@users.noreply.github.com>

tests/collections/ttables.nim

@@ -8,7 +8,6 @@ And we get here
 '''
 joinable: false
 targets: "c cpp js"
-matrix: "-d:nimEnableHashRef"
 """
 
 # xxx wrap in a template to test in VM, see https://github.com/timotheecour/Nim/issues/534#issuecomment-769565033

tests/config.nims

@@ -39,3 +39,4 @@ switch("define", "nimExperimentalLinenoiseExtra")
 switch("define", "nimPreviewFloatRoundtrip")
 switch("define", "nimPreviewDotLikeOps")
 switch("define", "nimPreviewJsonutilsHoleyEnum")
+switch("define", "nimPreviewHashRef")

tests/stdlib/thashes.nim

@@ -1,6 +1,5 @@
 discard """
   targets: "c cpp js"
-  matrix: "-d:nimEnableHashRef"
 """
 
 import std/hashes