Revert "Add header alignment attribute"

[hugovk]

Reverts #183

As detailed at #183 (comment), if there's no header_align value, it still changes the header alignment and ignores the align value:

In 3.3.0, the data and header were left-aligned.

In 3.4.0, only the data was left-aligned, the header was centre-aligned.

So let's revert and #183 can be resubmitted with a more robust fix.

[codecov]

Codecov Report

Merging #195 (2d727b2) into master (9553202) will decrease coverage by 0.10%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #195      +/-   ##
==========================================
- Coverage   94.14%   94.03%   -0.11%     
==========================================
  Files           5        5              
  Lines        2290     2248      -42     
==========================================
- Hits         2156     2114      -42     
  Misses        134      134              

Flag	Coverage Δ
macos-latest	94.03% <100.00%> (-0.11%)	⬇️
ubuntu-latest	94.03% <100.00%> (-0.11%)	⬇️
windows-latest	93.90% <100.00%> (-0.12%)	⬇️

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

Impacted Files	Coverage Δ
tests/test_prettytable.py	100.00% <ø> (ø)
src/prettytable/prettytable.py	90.19% <100.00%> (-0.21%)	⬇️

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more