Fix compiler warnings with Rust nightly

[satta]

• I have read the contributing guide lines at https://redmine.openinfosecfoundation.org/projects/suricata/wiki/Contributing
• I have signed the Open Information Security Foundation contribution agreement at https://suricata-ids.org/about/contribution-agreement/
• I have updated the user guide (in doc/userguide/) to reflect the changes made (if applicable)

Describe changes:

• Fix warnings with Rust nightly (rustc 1.55.0-nightly (406d4a9cc 2021-06-21)). These are simple changes relating to:
  • variables only used in debug output macros, which may be removed before compiling, making these variables unused, and
  • unused borrows in what should just be function calls.

[codecov]

Codecov Report

Merging #6216 (88b48ef) into master (b3c1f2a) will increase coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #6216      +/-   ##
==========================================
+ Coverage   76.95%   76.96%   +0.01%     
==========================================
  Files         611      611              
  Lines      186232   186233       +1     
==========================================
+ Hits       143306   143328      +22     
+ Misses      42926    42905      -21     

Flag	Coverage Δ
fuzzcorpus	52.92% <ø> (+0.01%)	⬆️
suricata-verify	51.13% <ø> (+0.05%)	⬆️
unittests	63.08% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

[catenacyber]

Looks good to me

Some part is duplicate with #6208

[satta]

Should be done via #6222

[satta]

Or do we want to keep this open since #6222 was only merged into the 6.x line?

[catenacyber]

I guess so

[victorjulien]

Merged in #6242, thanks!