quickstart: Remove "platform:" attribute from compose files

It is not necessary to specify a platform when pulling images, because
docker will default either to the host platform or amd64 with emulation
if a matching platform is not available.  Furthermore, since we will be
releasing ARM images soon, we do not want to specify AMD64 anymore.

Change-Id: I2d3b170d0a50ba4306142503f4bf19966a6a6964
Reviewed-on: https://gerrit.readyset.name/c/readyset/+/11418
Reviewed-by: Gautam Gopinadhan <gautam@readyset.io>
Tested-by: Buildkite CI

Author: ronh-rs

quickstart/compose.mysql.yml

@@ -2,7 +2,6 @@ name: readyset-mysql
 services:
   cache:
     image: docker.io/readysettech/readyset:latest
-    platform: linux/amd64
     ports:
       # The ReadySet Adapter listen port, i.e. what your application / SQL shell connects to
       - "3307:3307"

quickstart/compose.postgres.yml

@@ -2,7 +2,6 @@ name: readyset-postgres
 services:
   cache:
     image: docker.io/readysettech/readyset:latest
-    platform: linux/amd64
     ports:
       # The ReadySet Adapter listen port, i.e. what your application / SQL shell connects to
       - "5433:5433"

quickstart/compose.yml

@@ -2,7 +2,6 @@ name: readyset
 services:
   cache:
     image: "docker.io/readysettech/readyset:latest"
-    platform: linux/amd64
     ports:
       # The ReadySet Adapter listen port, i.e. what your application / SQL shell connects to
       - "5433:5433"