[LV2] More aggressive uri-map and event extensions deprecation

[David Robillard]

Hello everyone,

FYI, the next version of LV2 will more aggressively deprecate the uri-
map and event extensions, adding deprecated declaration warnings to
every symbol in their headers.  These have been deprecated for a long
time now, and I've noticed that new implementers tend to blindly copy
whatever is implemented in existing hosts, regardless of deprecation or
how widely they are used.

So, I've also removed support from Jalv entirely, and recommend that
other hosts do the same.

Cheers,

-- 
dr