Add back missing call to `resize`

The call to `resize` is pretty important... without it, nothing shows up
on the screen when I run flameshot (presumably because it's 0 pixels by
0 pixels large). This was accidentally removed when resolving merge
  conflicts in 77c509e7989b924d31d54e78c6f8e7a7e68968b9.

While I was in here, I also opted to delete some comments. I personally
am never a fan of commenting out code: if we need something, that's what
Git is for! And, just in case GitHub disappears, I thought it would be
nice to record my research in a Git commit about why I think removing
`Qt::BypassWindowManagerHint` is ok. Comments copied from
https://github.com/flameshot-org/flameshot/pull/731):

> I played around with it [removing `Qt::BypassWindowManagerHint`] a bit
> and it has some really nice properties for me as a Xmonad X11 user:
>
>   - It resolves https://github.com/flameshot-org/flameshot/issues/784
>   - It also makes it possible for me to clearly see when flameshot has
>     focus, and give it focus, which I'd argue is a workaround/fix for
> https://github.com/flameshot-org/flameshot/issues/1072, and also has
> some nice properties as @filipkilibarda mentioned: "Allows the user to
> switch workspaces while in the screenshot GUI..."
>
> I did some git spelunking and here's the history of the current code:
>
> - c4d9210c35025e328df57a10364c0da5570b1c15 is the first commit where
>   something like this showed up, but it used
> `Qt::X11BypassWindowManagerHint`, which is just [an alias for
> `Qt::BypassWindowManagerHint`](https://github.com/qt/qtbase/blob/b75d60abd2012d78387ec0751e205aef970a024b/src/corelib/global/qnamespace.h#L247)
> - 0f30529c77476e90ec49cc9abbf5bb6cdc422f6f removed it (yay!)
> - 11b0e2db4b4c0aadae9077622e9e2e72bb5d737f added in
>   `Qt::BypassWindowManagerHint` with somewhat cryptic message: "Capture
> window showing when mouse events are holded" message. I'm not sure what
> that means.
> - Later, this commit a9b0c213048259f20b95c0fb6599f3c318fa3234 added a
>   `#ifdef Q_OS_WIN`  branch that made it so this
> `Qt::BypassWindowManagerHint` only happens on Linux, not Windows.
>
> So, since flameshot doesn't currently target OSX, I think this change
> only affects Linux. @borgmanJeremy if I did some investigation into how
> this behaves with other window managers (and maybe wayland?) would you
> be open to merging it up?
> https://github.com/flameshot-org/flameshot/pull/731#issuecomment-719767364
> for more information.

Later, I investigated how things behave on Linux with a non-tiling
window manager:

> I just installed xfce and tried this out, and as far as I can tell,
> things work great! During a screenshot, I can alt-tab to other windows
> and they end up on top of the ongoing screenshot, but I can click back
> on the screenshot to continue editing the screenshot (strangely, I
> cannot alt-tab back to the window). Keyboard shortcuts work as expected,
> and this feels like an improvement in every way, IMO.

src/widgets/capture/capturewidget.cpp

@@ -136,10 +136,9 @@ CaptureWidget::CaptureWidget(const uint id,
         move(currentScreen->geometry().x(), currentScreen->geometry().y());
         resize(currentScreen->size());
 #else
-        // Disable Qt::BypassWindowManagerHint. Workaround for #583 #517
-        setWindowFlags(/* Qt::BypassWindowManagerHint */
-                       Qt::WindowStaysOnTopHint | Qt::FramelessWindowHint |
+        setWindowFlags(Qt::WindowStaysOnTopHint | Qt::FramelessWindowHint |
                        Qt::Tool);
+        resize(pixmap().size());
 #endif
     }
     // Create buttons