Fix #547 and revert #355

[tknopp]

With the new BB binaries the window decorations show correctly without setting GTK_CSD=1

close #547

@ping NeoKat75: I cannot test this, have you tested it with exactly this change?

[codecov]

Codecov Report

Merging #548 (007591d) into master (f879355) will increase coverage by 0.03%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #548      +/-   ##
==========================================
+ Coverage   49.94%   49.98%   +0.03%     
==========================================
  Files          32       32              
  Lines        2515     2513       -2     
==========================================
  Hits         1256     1256              
+ Misses       1259     1257       -2     

Impacted Files	Coverage Δ
src/Gtk.jl	88.46% <ø> (-0.83%)	⬇️
src/GLib/signals.jl	76.05% <0.00%> (+0.84%)	⬆️

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[NeoKat75]

@NeoKat75: I cannot test this, have you tested it with exactly this change?

@tknopp yep, it works just fine!