Fix msaa-line example's unnecessary MSAA data store

[jinleili]

Description
Storing pre-resolve MSAA data is unnecessary if it isn't used later. On tile-based GPU, avoid store can reduce app's memory footprint.

Testing
Tested on M1 macOS, Android 8.1 && 10.0 Phones(both GL and VULKAN backend), iPhone 12

Addition info

Debugging msaa-line example on macOS:

warning message：Storing pre-resolve MSAA data is unnecessary if it isn't used later. 

	

Debugging on iPhone:

warning message：Storing pre-resolve MSAA data is unnecessary if it isn't used later. 
It increases your app's memory footprint and can be avoided by using memoryless textures.

	

[kvark]

Nice!