Avoid using an alias variable.

[bangerth]

Looking into a function in FE_Q_Base, we initialize an array but do so by first
creating an alias (reference) variable for it and then writing into it.

I'm not a big fan of these alias variables. It makes it more difficult to read
code, and in particular to search code for where a variable is actually
initialized. (This is how I hit on this location.) I recognize that the variable
in question has a pretty long name, and that the lines become longer than we
usually like it, but IDEs typically show substantially more than 100 characters
per line these days, so I think the benefits outweigh the downsides.

This is ultimately a judgment call. The patch reflects my opinion,
but if others feel differently, then we can go that route as well.

[davydden]

/run-tests

[kronbichler]

In this case I'm certainly in favor of avoiding the alias.