rm copy of parseHex() from 1.2+ stdlib; some proc -> func

[tersec]

comparing it with https://github.com/nim-lang/Nim/blob/version-1-2/lib/pure/parseutils.nim#L156:

@@ -1,6 +1,5 @@
-# From: https://github.com/nim-lang/Nim/pull/11067/
-proc parseHex*[T: SomeInteger](s: string, number: var T, start = 0, maxLen = 0): int
-  {.inline, noSideEffect.} =
+proc parseHex*[T: SomeInteger](s: string, number: var T, start = 0,
+    maxLen = 0): int {.noSideEffect.} =
   ## Parses a hexadecimal number and stores its value in ``number``.
   ##
   ## Returns the number of the parsed characters or 0 in case of an error.

so unless the .inline. here but not in the stdlib version is important, they're identical, including formatting.