Remove support for arm and arm64 architecture

Signed-off-by: Tamal Saha <tamal@appscode.com>

Author: tamalsaha

Makefile

@@ -52,7 +52,7 @@ NEW_RESTIC_VER   := 0.9.5
 
 SRC_DIRS := cmd pkg # directories which hold app source (not vendored)
 
-DOCKER_PLATFORMS := linux/amd64 linux/arm linux/arm64
+DOCKER_PLATFORMS := linux/amd64
 BIN_PLATFORMS    := $(DOCKER_PLATFORMS)
 
 # Used internally.  Users should pass GOOS and/or GOARCH.