Remove `parking_lot` dependency

[madsmtm]

Fixes https://github.com/rust-windowing/winit/issues/650.

std's Mutex has recently improved a lot, so there's not really a performance argument for keeping i any more. Also means we won't have to use the same windows-sys version as parking_lot

Dependency tree (Windows):

// Before
winit v0.27.1
├── bitflags v1.3.2
├── instant v0.1.12
│   └── cfg-if v1.0.0
├── log v0.4.17
│   └── cfg-if v1.0.0
├── once_cell v1.13.0
├── parking_lot v0.12.1
│   ├── lock_api v0.4.7
│   │   └── scopeguard v1.1.0
│   │   [build-dependencies]
│   │   └── autocfg v1.1.0
│   └── parking_lot_core v0.9.3
│       ├── cfg-if v1.0.0
│       ├── smallvec v1.9.0
│       └── windows-sys v0.36.1
│           └── windows_x86_64_gnu v0.36.1
├── raw-window-handle v0.5.0
│   └── cty v0.2.2
└── windows-sys v0.36.1 (*)

// After
winit v0.27.1
├── bitflags v1.3.2
├── instant v0.1.12
│   └── cfg-if v1.0.0
├── log v0.4.17
│   └── cfg-if v1.0.0
├── once_cell v1.13.0
├── raw-window-handle v0.5.0
│   └── cty v0.2.2
└── windows-sys v0.36.1
    └── windows_x86_64_gnu v0.36.1

Dependency tree (X11):

// Before
winit v0.27.1
├── bitflags v1.3.2
├── instant v0.1.12
│   └── cfg-if v1.0.0
├── libc v0.2.129
├── log v0.4.17
│   └── cfg-if v1.0.0
├── mio v0.8.4
│   ├── libc v0.2.129
│   └── log v0.4.17 (*)
├── once_cell v1.13.0
├── parking_lot v0.12.1
│   ├── lock_api v0.4.7
│   │   └── scopeguard v1.1.0
│   │   [build-dependencies]
│   │   └── autocfg v1.1.0
│   └── parking_lot_core v0.9.3
│       ├── cfg-if v1.0.0
│       ├── libc v0.2.129
│       └── smallvec v1.9.0
├── percent-encoding v2.1.0
├── raw-window-handle v0.5.0
│   └── cty v0.2.2
└── x11-dl v2.20.0
    ├── lazy_static v1.4.0
    └── libc v0.2.129
    [build-dependencies]
    └── pkg-config v0.3.25

// After
winit v0.27.1
├── bitflags v1.3.2
├── instant v0.1.12
│   └── cfg-if v1.0.0
├── libc v0.2.129
├── log v0.4.17
│   └── cfg-if v1.0.0
├── mio v0.8.4
│   ├── libc v0.2.129
│   └── log v0.4.17 (*)
├── once_cell v1.13.0
├── percent-encoding v2.1.0
├── raw-window-handle v0.5.0
│   └── cty v0.2.2
└── x11-dl v2.20.0
    ├── lazy_static v1.4.0
    └── libc v0.2.129
    [build-dependencies]
    └── pkg-config v0.3.25

• [ ] Tested on all platforms changed
  • Nope, please test this!
• [x] Added an entry to CHANGELOG.md if knowledge of this change could be valuable to users
• [x] Updated documentation to reflect any user-facing changes, including notes of platform-specific behavior
• [x] Created or updated an example program if it would help users understand this functionality
• [x] Updated feature matrix, if new features were added or implemented