bugfix(cmd-use-clear) Removed automatic use of aliased firebase project

[hlshen]

@Memeriaj

Description

Before every command, applyRc runs. In applyRc, there exists a conditional check:

else if (!options.project && _.size(aliases) === 1) {
    options.projectAlias = _.head(_.keys(aliases));
    options.project = _.head(_.values(aliases));
  }

If there is no active project and there exists exactly one project with an alias, when running a command, the one project with an alias will be used.

This leads to some confusing logic. When a user runs firebase use --clear, they expect the active project to be cleared, but the current logic will lead to a false sense that the active project was never cleared.

Scenarios Tested

Scenarios:

1. User is using the one aliased project as the active project

   User runs firebase use --clear. User runs firebase use. The same *one aliased project shows up as the active project.

2. User has one aliased project and clears the active project

   Running a command will automatically use the one aliased project
   Running firebase use will show the one aliased project as the active project

3. When user has more than one aliased project, and clears the active project

   Running a command will see a "No Active Project" error message.
   Running firebase use will show that there is no active project.

[samtstern]

@mbleigh do you think this is still work pursuing>