inflation_history: repoint the "hosted on github" link too

Copilot caught a fourth reference this PR had missed: the narrative link
introducing the spreadsheet still pointed at this series own
lectures/datasets directory, which this PR empties. It would not have
404d -- the directory survives with other files -- it would have quietly
become wrong, which nothing would ever flag.

It now points at data-lectures CATALOG.md rather than a directory listing.
A reader following "hosted on github" gets the dataset registry: source,
licence, integrity status and which lectures consume each file. That is
strictly more useful than the folder it replaced, and the catalog is
generated from the manifests, so it cannot drift out of date.

Worth recording why the earlier sweep missed this. It searched for links
ENDING in a data-file extension, so a link to a DIRECTORY was invisible to
it -- a blind spot in the check for the audits blind spot. Re-sweeping
properly found two more of the same shape (inequality.md in both repos,
linking to the usa-gini builder notebook), which belong to a later wave.
Folded into QuantEcon/data-lectures#42.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: mmcky

lectures/inflation_history.md

@@ -79,7 +79,7 @@ In the present context, the  phrase "hard currency" means that the countries wer
 Under a gold or silver standard, some money also consisted of "warehouse certificates" that represented paper claims on gold or silver coins. Bank notes issued by the government or private banks can be viewed as examples of such "warehouse certificates".
 ```
 
-Let us bring the data into pandas from a spreadsheet that is [hosted on github](https://github.com/QuantEcon/lecture-python-intro/tree/main/lectures/datasets).
+Let us bring the data into pandas from a spreadsheet that is [hosted on github](https://github.com/QuantEcon/data-lectures/blob/main/CATALOG.md).
 
 ```{code-cell} ipython3
 # Import data and clean up the index