bug#25717: 25.1.1; "erc-button-google-url" should not refer to a specific search engine

[Andrew Robbins]

The ERC variable "erc-button-google-url" should not refer to a
specific search engine in its name and certainly not a
privacy-disrespecting one at that in a GNU program[1].

I would suggest renaming the variable to something more generic
such as "erc-button-web-search-url" or "erc-button-search-url"
and changing the default value from
"http://www.google.com/search?q=%s"; to any of the following (or
similar) at the developers' preference:

* "http://duckduckgo.com/?q=%s";
* "http://www.startpage.com/do/search?cat=web&query=%s";
* "http://www.ixquick.com/do/search?cat=web&query=%s";
* "http://search.yacy.net/yacysearch/index.html?query=%s"; (requires javascript)

[1] https://stallman.org/google.html

Cordially,
Andrew Robbins