Remove functions deprecated in 2.6.0

[Laerte]

The only deprecated logic that i didn't remove was:
- #5090

Because seems a little be tricky (should we remove the deprecated parameters?) 😄

I will commit the removal of #5090 logic later on in this PR.

[codecov]

Codecov Report

Merging #5996 (b112c72) into master (7c6aaed) will decrease coverage by 0.02%.
The diff coverage is n/a.

❗ Current head b112c72 differs from pull request most recent head 4ac7485. Consider uploading reports for the commit 4ac7485 to get more accurate results

@@            Coverage Diff             @@
##           master    #5996      +/-   ##
==========================================
- Coverage   89.23%   89.21%   -0.02%     
==========================================
  Files         163      162       -1     
  Lines       11370    11350      -20     
  Branches     1844     1843       -1     
==========================================
- Hits        10146    10126      -20     
  Misses        930      930              
  Partials      294      294              

Files Changed	Coverage Δ
scrapy/extensions/feedexport.py	95.61% <ø> (-0.04%)	⬇️
scrapy/squeues.py	100.00% <ø> (ø)

[wRAR]

should we remove the deprecated parameters?

I expected that we do, yeah. Do you think it's problematic?

[Laerte]

@wRAR Not at all! I will handle the leftover later then, i was just making sure, thanks man!

[Laerte]

@wRAR Seems something went off when we deprecated parameters from engine (is running for 4 hours already), can you please cancel the queued runs? 😅 My last commit reverts this change so i can take a look in a separate PR.

[Laerte]

Thanks @wRAR I will raise another PR to deprecate the spider parameter from engine soon as i understand what went off.