Fixes #4984 - Remove maximize from Meter (Metro) menu

[malcops]

Tested locally that the Meter menu does not have a maximize button, and cannot be resized.

First time contributor, and new to Qt.. any feedback is welcome of course.

[kdeng00]

Hey @malcops, funny enough I was working on the same issue as a first-time contributor. I fixed the sizing issue and was going to work on preventing the Meter window from being maximized but forgot the issue # then checked and to see that you made the commit.

[cassdeckard]

This fixes #4984 , no?

[malcops]

@mattdeckard yes it fixes #4984

[DomClark]

I don't think there's a need to keep a pointer to the subwindow in an m_subWindow member. It can stay local to showCustom.

[DomClark]

Can this be merged now, or does it still need testing? Also, the new code doesn't quite follow the coding conventions on spaces within parentheses, but does match the surrounding style.

@malcops If you edit the initial comment here to include the words "fixes #4984", GitHub will automatically close that issue when this pull request is merged.

Related issues are fixed.

[malcops]

@DomClark squashed the fixup commits and changed commit message. Left the spaces within parentheses as is, but let me know if you wanted that changed as well.