Replace concatenate with concat when merging from ctxs (#5305)
Replace concatenate with concat when merging from ctxs (#5305)

* replace concatenate with concat when merging from ctxs

* use as_in_context

Guneet-Dhillon/mxnet,Guneet-Dhillon/mxnet,Guneet-Dhillon/mxnet,Guneet-Dhillon/mxnet,Guneet-Dhillon/mxnet,Guneet-Dhillon/mxnet,Guneet-Dhillon/mxnet,Guneet-Dhillon/mxnet,Guneet-Dhillon/mxnet