refactor: Remove subspecs, merging them into the main spec

They cause complications by having their own TankerDeps dependency,
and we don't actually need them.
It's not like Utils or Storage are an optional feature of the lib.

Tanker/Tanker.podspec

@@ -17,28 +17,24 @@ It's available for browsers, desktop, iOS and Android.
   s.ios.deployment_target = '12.0'
   s.swift_version = '5.0'
 
-  s.source_files = 'Sources/TKR*', 'Headers/TKR*'
+  s.source_files = [
+    'Sources/TKR*', 'Headers/TKR*',
+    'Sources/Utils/*', 'Headers/Utils/*',
+    'Sources/Storage/*', 'Headers/Storage/*',
+    'Headers/ctanker/**/*.h', 'Headers/ctanker.h',
+    'Headers/Tanker-umbrella.h'
+  ]
   s.private_header_files = 'Headers/*+Private.h'
+
   s.pod_target_xcconfig = {
     'USE_HEADERMAP' => "NO",
     'DEFINES_MODULE' => "YES",
   }
 
-
   s.header_mappings_dir = 'Headers'
   s.vendored_framework = 'Frameworks/TankerDeps.xcframework'
   s.preserve_paths = 'Tests/Dummy.m'
 
-  s.subspec 'Utils' do |utils_spec|
-    utils_spec.source_files = 'Sources/Utils/*', 'Headers/Utils/*'
-    utils_spec.vendored_framework = 'Frameworks/TankerDeps.xcframework'
-  end
-
-  s.subspec 'Storage' do |storage_spec|
-    storage_spec.source_files = 'Sources/Storage/*', 'Headers/Storage/TKR*'
-    storage_spec.dependency 'Tanker/Utils'
-  end
-
   s.test_spec 'Tests' do |test_spec|
     test_spec.source_files = 'Tests/*.{h,m,swift}'
     test_spec.exclude_files = 'Tests/TankerTests-Bridging-Header.h'