wxBitmap with cleared alpha channel doesn't keep its alpha flag any more.

Explicitly reset wxBitmap alpha flag after clearing its alpha channel to
ensure that we don't treat it as having alpha after going to all the trouble
of ensuring that it doesn't/

See #14403.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@75588 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
Remove commented out line from the dnd sample.

No real changes, just remove the unnecessary line and its outdated comment
(wxPaintDC::Clear() can be called in wxGTK, it's just not useful).

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@75589 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
Don't use deprecated wxBOLD, wxNORMAL and similar constants.

Replace them with wxFONTWEIGHT_BOLD, wxFONTSTYLE_NORMAL or wxFONTWEIGHT_NORMAL
and equivalents in the code of the library itself and in the samples.

Also simplify font construction using wxFontInfo where possible to avoid
specifying these constants at all if they are not needed.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@75590 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775