remove ncli re import/libpcre dependency

[tersec]

https://nim-lang.org/docs/re.html is

implemented by providing a wrapper around the PCRE (Perl-Compatible Regular Expressions) C library.

In particular, https://github.com/nim-lang/Nim/blob/8ccde68f132be4dba330eb6ec50f4679e564efac/lib/wrappers/pcre.nim#L313-L329 pulls in libpcre using some system and configuration-dependent method:

when not defined(usePcreHeader):
  when hostOS == "windows":
    when defined(nimOldDlls):
      const pcreDll = "pcre.dll"
    elif defined(cpu64):
      const pcreDll = "pcre64.dll"
    else:
      const pcreDll = "pcre32.dll"
  elif hostOS == "macosx":
    const pcreDll = "libpcre(.3|.1|).dylib"
  else:
    const pcreDll = "libpcre.so(.3|.1|)"
  {.push dynlib: pcreDll.}
else:
  {.push header: "<pcre.h>".}

{.push cdecl, importc: "pcre_$1".}

nimbus-eth doesn't otherwise seem to use the re module, so this should remove the its last vestige, and keep nimbus-eth2 free of such dependency hazards.

Otherwise, when running ncli_db without a supported version of libpcre (not a documented requirement):

nimbus-eth2$ build/ncli_db 
could not load: libpcre.so(.3|.1|)
compile with -d:nimDebugDlOpen for more information

[jakubgs]

I checked out this bizarrely named anO branch and it appears to fix the could not load: libpcre.so(.3|.1|) error:

~/work/nimbus-eth2 anO
 > make ncli_db -j12
Building: install/usr/lib/libbacktracenim.a
Building: build/generate_makefile
Build completed successfully: build/generate_makefile
Building: build/ncli_db
Build completed successfully: build/ncli_db

~/work/nimbus-eth2 anO
 > build/ncli_db --help   
Usage: 

ncli_db [OPTIONS]... command

The following options are available:

 --db           Directory where `nbc.sqlite` is stored.
 --network      The Eth2 network preset to use.
...

Thanks!