[libc][NFC] Remove allocator definition in the api-test.

The integration tests already have allocators so we will get all of them
from there.

Author: Siva Chandra Reddy

libc/test/IntegrationTest/test.cpp

@@ -29,4 +29,9 @@ void *malloc(size_t s) {
 
 void free(void *) {}
 
+void *realloc(void *ptr, size_t s) {
+  free(ptr);
+  return malloc(s);
+}
+
 } // extern "C"

libc/utils/HdrGen/PrototypeTestGen/PrototypeTestGen.cpp

@@ -95,12 +95,6 @@ bool TestGeneratorMain(llvm::raw_ostream &OS, llvm::RecordKeeper &records) {
   OS << "  return 0;\n";
   OS << "}\n\n";
 
-  // We provide dummy malloc and free implementations to support the case
-  // when LLVM libc does to include them.
-  OS << "void *malloc(size_t) __NOEXCEPT { return nullptr; }\n";
-  OS << "void *realloc(void *, size_t) __NOEXCEPT { return nullptr; }\n";
-  OS << "void free(void *) __NOEXCEPT {}\n";
-
   return false;
 }