Revert "Also run git gc after nvm upgraded"

This reverts commit ce7f6d6e52.

install.sh

@@ -74,10 +74,6 @@ install_nvm_from_git() {
       echo >&2 "Failed to update nvm, run 'git fetch' in $INSTALL_DIR yourself."
       exit 1
     }
-    echo "=> Compressing and cleaning up git repository"
-    if ! command git --git-dir="$INSTALL_DIR"/.git --work-tree="$INSTALL_DIR" gc --aggressive --prune=now ; then
-      echo >&2 "Your version of git is out of date. Please update it!"
-    fi
   else
     # Cloning to $INSTALL_DIR
     echo "=> Downloading nvm from git to '$INSTALL_DIR'"