fix: remove the broken golangci-lint cache path

.gitignore

@@ -37,6 +37,3 @@ Thumbs.db
 
 # Test reports
 *-report.txt
-
-# Per-worktree golangci-lint cache
-/.cache/

Makefile

@@ -1,11 +1,6 @@
 GO_PROJECT_NAME := spx
 SHELL := /bin/bash
 
-# golangci-lint's default cache (~/.cache/golangci-lint) is keyed by module
-# path, not worktree path, so parallel worktrees of this module collide and
-# surface each other's issues. Scope it per worktree.
-export GOLANGCI_LINT_CACHE := $(CURDIR)/.cache/golangci-lint
-
 # GOFIPS140 is a global build-config change: it alters every package's action ID,
 # stdlib included, so a target that omits it shares no build-cache entry with one
 # that sets it. Exported once here rather than per-recipe so the two can't drift.