Ubuntu: Remove QCommandLineParser options from src/Ubuntu/main.cpp

For some reason UbuntuTouch/Unity8 require --desktop_file_hint
and --stage_hint to be passed when launching an app. Which
the commandline parser was blocking these args. Since the
commandline options were only really just setting the size of
the qquickview we can safely just remove it and stick to a fixed
size window.

Removed associated context properties from main.qml

REVIEW: 118429