QbsProjectManager: Do not offer to remove qbs files in context menu.
QbsProjectManager: Do not offer to remove qbs files in context menu.

Such build system files must be filtered out, as they do not appear on
the right-hand side of "files" properties and have completely different
remove semantics.

Change-Id: I3963aa853003f4d674392434529dab19749af25b
Reviewed-by: Joerg Bornemann <47777b9406dbddd02a3fdca8341789a013805a11@digia.com>

danimo/qt-creator,farseerri/git_code,kuba1/qtcreator,AltarBeastiful/qt-creator,xianian/qt-creator,danimo/qt-creator,farseerri/git_code,xianian/qt-creator,amyvmiwei/qt-creator,AltarBeastiful/qt-creator,danimo/qt-creator,xianian/qt-creator,farseerri/git_code,kuba1/qtcreator,kuba1/qtcreator,farseerri/git_code,AltarBeastiful/qt-creator,AltarBeastiful/qt-creator,Distrotech/qtcreator,farseerri/git_code,AltarBeastiful/qt-creator,danimo/qt-creator,AltarBeastiful/qt-creator,martyone/sailfish-qtcreator,martyone/sailfish-qtcreator,xianian/qt-creator,martyone/sailfish-qtcreator,kuba1/qtcreator,amyvmiwei/qt-creator,danimo/qt-creator,amyvmiwei/qt-creator,kuba1/qtcreator,kuba1/qtcreator,Distrotech/qtcreator,danimo/qt-creator,danimo/qt-creator,martyone/sailfish-qtcreator,martyone/sailfish-qtcreator,xianian/qt-creator,Distrotech/qtcreator,farseerri/git_code,danimo/qt-creator,xianian/qt-creator,farseerri/git_code,amyvmiwei/qt-creator,xianian/qt-creator,amyvmiwei/qt-creator,Distrotech/qtcreator,kuba1/qtcreator,Distrotech/qtcreator,xianian/qt-creator,kuba1/qtcreator,xianian/qt-creator,Distrotech/qtcreator,martyone/sailfish-qtcreator,amyvmiwei/qt-creator,amyvmiwei/qt-creator,farseerri/git_code,AltarBeastiful/qt-creator,martyone/sailfish-qtcreator,Distrotech/qtcreator,danimo/qt-creator,AltarBeastiful/qt-creator,amyvmiwei/qt-creator,martyone/sailfish-qtcreator,martyone/sailfish-qtcreator,kuba1/qtcreator