Function Get-GmailAlias ($ID) {
$a = (Get-RemoteMailbox $ID | Select-Object DisplayName,PrimarySmtpAddress, @{ Name="EmailAddresses"; Expression={$_.EmailAddresses | Where-Object { $_.PrefixString -ceq "smtp" } | ForEach-Object { $_.SmtpAddress }}}).EmailAddresses | Where-Object { $_ -like '*gmail*' }

$b=@()
foreach ($mem in $a) {
    $b += "'$mem'"
}
$c= $b -join ', '
return $c

'kiran.kumar@gmail.com', 'kiran_kumar@gmail.com'

Set-RemoteMailbox kpv@gmail.com -EmailAddresses @{Remove=Get-GmailAlias('kpv@gmail.com')}

WARNING: The command completed successfully but no settings of 'XXX/XXX/XXX/XXX/XXX/XXX/Kiran Kumar' have been modified.

>@{Remove=$(Get-GmailAlias('kpv@gmail.com'))} # Alternative-1
>$c = Get-GmailAlias('kpv@gmail.com')
@{Remove="$c"} # Alternative-2
>$c = "@{Remove = $(Get-GmailAlias('kpv@gmail.com'))}"
Set-RemoteMailbox kpv@gmail.com -EmailAddresses $c # Alternative-3

Cannot process argument transformation on parameter 'EmailAddresses'. Cannot convert value "@{Remove = 'kiran.kumar@gmail.com', 'kiran_kumar@gmail.com'}" to type "Microsoft.Exchange.Data.ProxyAddressCollection".