configure: remove php test

+ the remnants in the build system & README

the documentation that required php was removed in:
50fa585 Removing examples code generation and making them static.

Change-Id: Ibf00dca9ab2715fc21e8de358807b63d1445662c
diff --git a/configure b/configure
index af3de7b..bd95056 100755
--- a/configure
+++ b/configure
@@ -189,7 +189,7 @@
 # install everything except the sources, by default. sources will have
 # to be enabled when doing dist builds, since that's no longer a common
 # case.
-enabled doxygen && php -v >/dev/null 2>&1 && enable_feature install_docs
+enabled doxygen && enable_feature install_docs
 enable_feature install_bins
 enable_feature install_libs