Remove unneeded forward declarations. NFC (#18268)

Author: sbc100

system/lib/compiler-rt/lib/lsan/lsan_common.cpp

@@ -27,6 +27,7 @@
 
 #if SANITIZER_EMSCRIPTEN
 #include "lsan/lsan_allocator.h"
+#include "emscripten/heap.h"
 #endif
 
 #if CAN_SANITIZE_LEAKS
@@ -531,10 +532,6 @@ void ScanRootRegion(Frontier *frontier, const RootRegion &root_region,
                          kReachable);
 }
 
-#if SANITIZER_EMSCRIPTEN
-extern "C" uptr emscripten_get_heap_size();
-#endif
-
 static void ProcessRootRegion(Frontier *frontier,
                               const RootRegion &root_region) {
 #if SANITIZER_EMSCRIPTEN

system/lib/compiler-rt/lib/lsan/lsan_common_emscripten.cpp

@@ -33,8 +33,6 @@
 
 namespace __lsan {
 
-extern "C" uptr emscripten_get_heap_size();
-
 static const char kLinkerName[] = "ld";
 
 static char linker_placeholder[sizeof(LoadedModule)] ALIGNED(64);