cmd/utils: avoid making console preloads absolute (#22109)

Resolves https://github.com/etclabscore/core-geth/issues/273



jsre.JSRE already handles establishing preload
file paths relative to the 'assets' path (aka docroot),
where it joins the assets dir and the file path if relative,
or uses the file path only if absolute.

The duplication of this logic by MakeConsolePreloads
caused preloaded files to have paths which contained
duplicate references to the assets dir path.

Date: 2020-12-30 08:25:01-06:00
Signed-off-by: meows <b5c6@protonmail.com>