Remove <signal.h> inlines for obsolete API levels.

The next NDK to take these headers only supports API 21 and later.

Test: treehugger
Change-Id: I8fe617e6eb781629ddf0b98b0037a9b3e54c559c
diff --git a/libc/bionic/__libc_current_sigrtmax.cpp b/libc/bionic/__libc_current_sigrtmax.cpp
index 32179bb..328ede1 100644
--- a/libc/bionic/__libc_current_sigrtmax.cpp
+++ b/libc/bionic/__libc_current_sigrtmax.cpp
@@ -28,8 +28,6 @@
 
 #include <signal.h>
 
-int __libc_current_sigrtmax(void) {
-  // If you change this, also change __ndk_legacy___libc_current_sigrtmax
-  // in <android/legacy_signal_inlines.h> to match.
+int __libc_current_sigrtmax() {
   return __SIGRTMAX;
 }