Issue 8101 - Fixup pull improving diagnostics when there are overloads present.

This is a small fixup for the diagnostic introduced in https://github.com/D-Programming-Language/dmd/pull/3508.

https://issues.dlang.org/show_bug.cgi?id=8101

Essentially we don't have to print the argument types of a single function when there are multiple overloads listed.

Another future improvement that could be done is to detect `@property` functions. If the only overloads are properties then the diagnostic could reflect that.