Remove-AzRoleAssignment : Multiple role definitions found with name ''

## Description

If a scope has multiple role assignments with an empty RoleDefinitionName, then Remove-AzRoleAssignment will fail with the following error:

PS C:\Users\kwill> $DeprecatedAccounts[0] | Remove-AzRoleAssignment
Remove-AzRoleAssignment : Multiple role definitions found with name ''. Specify role definition using it's Id instead.
At line:1 char:26

$DeprecatedAccounts[0] | Remove-AzRoleAssignment
~~~~~~~~~~~~~~~~~~~~~~~
CategoryInfo : CloseError: (:) [Remove-AzRoleAssignment], InvalidOperationException
FullyQualifiedErrorId : Microsoft.Azure.Commands.Resources.RemoveAzureRoleAssignmentCommand

To fix, RemoveAzureRoleAssignmentCommand.cs should include the roleDefinitionId in this section of code:
if (this.IsParameterBound(c => c.InputObject))
{
Scope = InputObject.Scope;
ObjectId = InputObject.ObjectId;
RoleDefinitionName = InputObject.RoleDefinitionName;
}

Start in RemoveAzureRoleAssignmentCommand.cs at the InputObject parameter-bound block and reproduce the failure with multiple role assignments whose RoleDefinitionName is empty. Trace how the input object's role definition identifier is handled there, then verify that piping the assignment to Remove-AzRoleAssignment succeeds without the ambiguous-name error.

Written by the indexing model from the issue text.