aws: use AWS_CONFIG_FILE to complete profiles

Stop exporting AWS_HOME and use the standard AWS_CONFIG_FILE environment
variable, with a fallback to ~/.aws/config (default location) if not
defined.

Close #7356

plugins/aws/aws.plugin.zsh

@@ -21,8 +21,6 @@ _awscli-homebrew-installed() {
   [ -r $_brew_prefix/libexec/bin/aws_zsh_completer.sh ] &> /dev/null
 }
 
-export AWS_HOME=~/.aws
-
 function agp {
   echo $AWS_PROFILE
 }
@@ -37,7 +35,7 @@ function asp {
 }
 
 function aws_profiles {
-  reply=($(grep profile $AWS_HOME/config|sed -e 's/.*profile \([a-zA-Z0-9_\.-]*\).*/\1/'))
+  reply=($(grep profile "${AWS_CONFIG_FILE:-$HOME/.aws/config}"|sed -e 's/.*profile \([a-zA-Z0-9_\.-]*\).*/\1/'))
 }
 compctl -K aws_profiles asp