remove nvm installation for SDK automation (#30607)

fixes https://github.com/Azure/azure-sdk-tools/issues/7967

.scripts/automation_generate.sh

@@ -1,5 +1,2 @@
 #!/usr/bin/env bash
-export NVM_DIR="$HOME/.nvm"
-[ -s "$NVM_DIR/nvm.sh" ] && \. "$NVM_DIR/nvm.sh" # This loads nvm
-nvm use default
 code-gen-pipeline --inputJsonPath=$1 --outputJsonPath=$2 --use=@autorest/typescript@^6.0.12 --typespecEmitter=@azure-tools/typespec-ts

.scripts/automation_init.sh

@@ -1,8 +1,4 @@
 #!/usr/bin/env bash
-curl -o- https://raw.githubusercontent.com/nvm-sh/nvm/v0.39.3/install.sh | bash
-export NVM_DIR="$HOME/.nvm"
-[ -s "$NVM_DIR/nvm.sh" ] && \. "$NVM_DIR/nvm.sh" # This loads nvm
-nvm install v18.15.0 
-nvm alias default node
+npm install -g @azure-tools/typespec-client-generator-cli
 npm install -g @microsoft/rush@5.92.0
 npm install -g @azure-tools/js-sdk-release-tools