chore(php-shim): drop the ob_start()/ob_get_clean() ports

Output buffering captures whatever the PHP interpreter would echo to
stdout. The shim routes no output through a buffer, so these functions
could never capture anything and stayed todo!(). Record the gap in
docs/known-incompatibilities.md instead.

1 files changed, 5 insertions, 0 deletions

diff --git a/docs/known-incompatibilities.md b/docs/known-incompatibilities.md
index 97e4dad7..e8e6a038 100644
--- a/docs/known-incompatibilities.md
+++ b/docs/known-incompatibilities.md
@@ -59,3 +59,8 @@ read or written through `ReflectionProperty`; only the public methods reach the
 `ReflectionClass::getFileName()` and the method bodies do not describe Composer's sources either.
 
 Reflection on objects a plugin creates itself works as usual.
+
+### Output buffering functions
+
+`ob_*()` functions work as usual in PHP, but cannot capture any output from
+Rust side.