log: remove log "module" system

After comtemplation, the complexity of the logging module system
outweighs its usefulness. This changeset removes the system and restores
lighter weight code paths. As a concession, we can always provide more
context when necessary to log messages to understand them without having
to fork the context for a certain set of calls.

Signed-off-by: Stephen J Day <stephen.day@docker.com>

log/context_test.go

@@ -16,26 +16,3 @@ func TestLoggerContext(t *testing.T) {
 	assert.Equal(t, GetLogger(ctx).Data["test"], "one")
 	assert.Equal(t, G(ctx), GetLogger(ctx)) // these should be the same.
 }
-
-func TestModuleContext(t *testing.T) {
-	ctx := context.Background()
-	assert.Equal(t, GetModulePath(ctx), "")
-
-	ctx = WithModule(ctx, "a") // basic behavior
-	assert.Equal(t, GetModulePath(ctx), "a")
-	logger := GetLogger(ctx)
-	assert.Equal(t, logger.Data["module"], "a")
-
-	parent, ctx := ctx, WithModule(ctx, "a")
-	assert.Equal(t, ctx, parent) // should be a no-op
-	assert.Equal(t, GetModulePath(ctx), "a")
-	assert.Equal(t, GetLogger(ctx).Data["module"], "a")
-
-	ctx = WithModule(ctx, "b") // new module
-	assert.Equal(t, GetModulePath(ctx), "a/b")
-	assert.Equal(t, GetLogger(ctx).Data["module"], "a/b")
-
-	ctx = WithModule(ctx, "c") // new module
-	assert.Equal(t, GetModulePath(ctx), "a/b/c")
-	assert.Equal(t, GetLogger(ctx).Data["module"], "a/b/c")
-}