Revert "SL-19338: (WIP) Test disabling new use of glTexSubImage2D and see if the bug still repros"

This reverts commit 6c486e4853.

indra/llrender/llimagegl.cpp

@@ -1408,9 +1408,7 @@ void LLImageGL::setManualImage(U32 target, S32 miplevel, S32 intformat, S32 widt
         LL_PROFILE_ZONE_NUM(height);
 
         free_cur_tex_image();
-// TODO: Revert
-//#if LL_DARWIN
-#if 1
+#if LL_DARWIN
         {
             LL_PROFILE_ZONE_NAMED("glTexImage2D alloc");
             glTexImage2D(target, miplevel, intformat, width, height, 0, pixformat, pixtype, use_scratch ? scratch : pixels);