Remove ubuntu-specific instruction from rpm guide

Though the bug report notes the step is obsolete for grizzly,
it was from the yum/rpm guide, and it was an ubuntu specific instruction

This change modifies the paragraph so the ubuntu-specific instruction is
only shown where it belongs.

fixes bug 1199625

Change-Id: Iba80183bbf140eccaa835cc8a8cc2a123edf444c
Merge "Remove ubuntu-specific instruction from rpm guide"