Remove border from Qt HeadingText.

[corranwebster]

Fixes #664

[codecov-commenter]

Codecov Report

Merging #692 into master will increase coverage by 0.07%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #692      +/-   ##
==========================================
+ Coverage   39.72%   39.80%   +0.07%     
==========================================
  Files         492      492              
  Lines       27222    27220       -2     
  Branches     4134     4134              
==========================================
+ Hits        10815    10835      +20     
+ Misses      15935    15921      -14     
+ Partials      472      464       -8     

Impacted Files	Coverage Δ
pyface/ui/qt4/heading_text.py	90.47% <ø> (-0.83%)	⬇️
pyface/ui/qt4/console/console_widget.py	29.28% <0.00%> (+0.20%)	⬆️
pyface/ui/qt4/code_editor/code_widget.py	44.16% <0.00%> (+0.84%)	⬆️
pyface/wx/python_stc.py	10.36% <0.00%> (+1.21%)	⬆️
pyface/ui/wx/window.py	77.10% <0.00%> (+2.40%)	⬆️
pyface/ui/qt4/util/gui_test_assistant.py	80.53% <0.00%> (+2.65%)	⬆️
pyface/ui/wx/data_view/data_view_widget.py	77.52% <0.00%> (+5.61%)	⬆️
pyface/__init__.py	88.88% <0.00%> (+7.40%)	⬆️
pyface/i_file_dialog.py	84.61% <0.00%> (+7.69%)	⬆️

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[rahulporuri]

LGTM