censor: remove meaningless explanation about .hgcensored

There is no code path handling ".hgcensored" in Mercurial source tree.

This meaningless explanation may make users misunderstand about
censor.

hgext/censor.py

@@ -17,12 +17,6 b' Typical uses for censor are due to secur'
  * Licensed data/code/libraries for which the license has expired
  * Personally Identifiable Information or other private data
 
-Censored file revisions are listed in a tracked file called .hgcensored stored
-in the repository root. The censor command adds an entry to the .hgcensored file
-in the working directory and commits it (much like ``hg tag`` and .hgtags). The
-censored file data is then replaced with a pointer to the new commit, enabling
-verification.
-
 Censored nodes can interrupt mercurial's typical operation whenever the excised
 data needs to be materialized. Some commands, like ``hg cat``/``hg revert``,
 simply fail when asked to produce censored data. Others, like ``hg verify`` and