Stepping down as Cortex maintainer (#6082)

I can't believe this day would come, but I am stepping down as Cortex maintainer because I no longer have capacity to give Cortex the love it needs anymore. Also, Cortex is in good hands with existing maintainers from diverse set of companies.

It's been a fun ride. I still remember my [first Cortex PR](#2741) that allows me to build Cortex in my employer's network, and [the day I became maintainer 3 years ago](b4daa22). It was full of joys and emotions. But there is always an end to a party, and for me it's today. 

Thank you all for the great work and support thus far!

Signed-off-by: Alvin Lin <[email protected]>

Author: alvinlin123

MAINTAINERS

@@ -1,5 +1,4 @@
 Alan Protasio, Amazon Web Services <[email protected]> (@alanprot)
-Alvin Lin, Amazon Web Services <[email protected]> (@alvinlin123)
 Ben Ye, Amazon Web Services <[email protected]> (@yeya24)
 Charlie Le, Apple <[email protected]> (@CharlieTLe)
 Daniel Blando, Amazon Web Services <[email protected]> (@danielblando)