refactor: remove gimme and run_with_go_ver script (#13415)

Now that we have a toolchain directive explicitly defined in go.mod
we can drop gimme and the shell script to ensure we are running the
correct go version

Tiltfile

@@ -98,11 +98,10 @@ if config.tilt_subcommand == "down":
   print(local("kubectl delete --ignore-not-found namespace/elastic-system"))
 
 # Add a button for sending trace events and metrics to APM Server.
-run_with_go_ver = os.path.join(script_dir, 'run_with_go_ver')
 load('ext://uibutton', 'cmd_button')
 cmd_button(
   'apm-server:sendotlp',
-  argv=['sh', '-c', 'cd systemtest && %s go run ./cmd/sendotlp' % run_with_go_ver],
+  argv=['sh', '-c', 'cd systemtest && go run ./cmd/sendotlp'],
   resource='apm-server',
   icon_name='input',
   text='Send OTLP data',

go.mk

@@ -5,10 +5,9 @@ GITCOMMITTIMESTAMPUNIX ?= $(shell git log -1 --pretty=%ct)
 GITREFFILE ?= $(GITDIR)/$(shell git rev-parse --symbolic-full-name HEAD)
 GITROOT ?= $(shell git rev-parse --show-toplevel)
 
-# Ensure the Go version in .go-version is installed and used.
-GOROOT?=$(shell $(GITROOT)/script/run_with_go_ver go env GOROOT)
+GOROOT?=$(go env GOROOT)
 GOLANG_VERSION=$(shell cat $(GITROOT)/.go-version)
-GO:=$(GOROOT)/bin/go
+GO:=go
 GOARCH:=$(shell $(GO) env GOARCH)
 export PATH:=$(GOROOT)/bin:$(PATH)