Revert "Made hidl_vec(size_t size) explicit"

This reverts commit f7e10f4a46ab6343b72d0a1e948d029a6a8be3ba.
That commit broke several builds.

I suspect that an implicit conversion now made explicit has exposed
several issues where a hidl_vec not was constructed correctly, but not
entirely sure.

Test: That it builds
diff --git a/base/include/hidl/HidlSupport.h b/base/include/hidl/HidlSupport.h
index 98b37ab..55f21ea 100644
--- a/base/include/hidl/HidlSupport.h
+++ b/base/include/hidl/HidlSupport.h
@@ -334,7 +334,7 @@
     }
 
     // Note, does not initialize primitive types.
-    explicit hidl_vec(size_t size) : hidl_vec() { resize(size); }
+    hidl_vec(size_t size) : hidl_vec() { resize(size); }
 
     hidl_vec(const hidl_vec<T> &other) : hidl_vec() {
         *this = other;