Delete avatar link is showing even if no avatar was uploaded

[imath]

Since ​7769 bp_get_user_has_avatar() returns true even if the user haven't uploaded an avatar.
As a result, in change-avatar screen and in the /wp-admin community profile, the link to delete the avatar is showing.
The diff attached seems to solve the issue.

[boonebgorges]

Looks good to me. Let's write a unit test so that this doesn't get broken again.

[imath]

While working on #5429, i've noticed the bp_get_group_has_avatar() also needed to be adapted. In 5380.01.diff I've included a group id argument to be able to check even if the current group is not set.

[boonebgorges]

In 8243:

Ensure bp_get_user_has_avatar() returns false when the default avatar is returned

Necessitated by changes in return values introduced in r7769

See #5380

Props imath

[boonebgorges]

In 8244:

Allow bp_get_group_has_avatar() to accept a group_id param

Also fix some logic that was causing the function to return true when the
group avatar matched the default avatar (meaning that no local avatar had been
uploaded). See r7769

Fixes #5380

Props imath