build: remove --enable-experimental-features / EXPERIMENTAL_FEATURES

Changelog-EXPERIMENTAL: Build: all experimental features are now runtime-enabled; no more ./configure --enable-experimental-features
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

doc/FUZZING.md

@@ -24,7 +24,7 @@ a few sanitizers for bug detections as well as experimental features for an exte
 coverage (not required though).
 
 ```
-./configure --enable-developer --enable-experimental-features --enable-address-sanitizer --enable-ub-sanitizer --enable-fuzzing --disable-valgrind CC=clang && make
+./configure --enable-developer --enable-address-sanitizer --enable-ub-sanitizer --enable-fuzzing --disable-valgrind CC=clang && make
 ```
 
 The targets will be built in `tests/fuzz/` as `fuzz-` binaries, with their best

doc/STYLE.md

@@ -236,7 +236,7 @@ have a line with one of the following prefixes:
    not yet removed
  - `Changelog-Fixed: ` if a bug has been fixed
  - `Changelog-Removed: ` if a (previously deprecated) feature has been removed
- - `Changelog-Experimental: ` if it only affects --enable-experimental-features builds, or experimental- config options.
+ - `Changelog-Experimental: ` if it only affects experimental- config options.
  
 In case you think the pull request is small enough not to require a changelog
 entry please use `Changelog-None` in one of the commit messages to opt out.

doc/lightningd-config.5.md

@@ -664,28 +664,18 @@ considered important.
 
 Experimental options are subject to breakage between releases: they
 are made available for advanced users who want to test proposed
-features. When the build is configured _without_ `--enable-experimental-features`,
-below options are available but disabled by default.
-Supported features can be listed with `lightningd --list-features-only`
-
-A build _with_ `--enable-experimental-features` flag hard-codes some of below
-options as enabled, ignoring their command line flag. It may also add support for
-even more features. The safest way to determine the active configuration is by
-checking `listconfigs` or by looking at `our_features` (bits) in `getinfo`.
+features.
 
 * **experimental-onion-messages**
 
   Specifying this enables sending, forwarding and receiving onion messages,
 which are in draft status in the [bolt][bolt] specifications (PR #759).
-A build with `--enable-experimental-features` usually enables this via
-experimental-offers, see below.
+This is automatically enabled by `experimental-offers`.
 
 * **experimental-offers**
 
   Specifying this enables the `offers` and `fetchinvoice` plugins and
-corresponding functionality, which are in draft status ([bolt][bolt] #798) as [bolt12][bolt12].
-A build with `--enable-experimental-features` enables this permanently and usually
-enables experimental-onion-messages as well.
+corresponding functionality, which are in draft status ([bolt][bolt] #798) as [bolt12][bolt12], as well as `experimental-onion-messages`.
 
 * **fetchinvoice-noconnect**