Custom-reset-standard has different menu names

[Drew Adams]

I believe that `Custom-reset-standard' resets the current setting of a
preference (face or variable) to the installed (standard) setting, and
it also updates the user's custom-file to reflect this. That is, it
removes any saved customization for the preference.

Perhaps this updating of the custom-file is the reason that this
particular resetting is the only one that is not called "Reset"... If
so, "Erase Customization" is not more clear - it can give the opposite
impression that it just erases editing or setting changes in the
Customize buffer.

Anyway, the bug is that this function has 3 menu names, one of which
is different from the other two:

 - Erase Customization (use standard settings) -- on the Reset menu
 - Erase Customization                         -- push button
 - Reset to Standard Settings                  -- menu-bar menu

And in the mode doc string (`custom-mode') it is said to "Reset all
options".

A single pretty name should be used for this in all places. The name
used in Emacs 20, "Reset to Standard" seems clearer than "Erase
Customization".