fix: removes net6 from install scripts

Author: leonardochaia

eng/install-sdk.ps1

@@ -10,5 +10,4 @@ $globalJsonFile = "$PSScriptRoot\..\global.json"
 $dotnetInstallDir = "$PSScriptRoot\.dotnet"
 
 . $installScript  -InstallDir $dotnetInstallDir -JSonFile $globalJsonFile
-. $installScript  -InstallDir $dotnetInstallDir -Channel 6.0
 . $installScript  -InstallDir $dotnetInstallDir -Channel 8.0

eng/install-sdk.sh

@@ -14,5 +14,4 @@ global_json_file="$(dirname "$0")/../global.json"
 dotnet_install_dir="$(dirname "$0")/.dotnet"
 
 "$install_script" --install-dir "$dotnet_install_dir" --jsonfile "$global_json_file"
-"$install_script" --install-dir "$dotnet_install_dir" --channel 6.0
 "$install_script" --install-dir "$dotnet_install_dir" --channel 8.0