2.x Remove unneeded Timber\Image::is_image() method #879

Job	Run time
PHP 7.4 \| WP latest \| highest	2m 28s
PHP 7.4 \| WP latest \| lowest	2m 21s
PHP 7.4 \| WP latest (MS) \| highest	2m 45s
PHP 7.4 \| WP latest (MS) \| lowest	3m 19s
PHP 7.4 \| WP 5.3 \| highest	3m 7s
PHP 7.4 \| WP 5.3 \| lowest	2m 29s
PHP 7.4 \| WP 5.3 (MS) \| highest	3m 10s
PHP 7.4 \| WP 5.3 (MS) \| lowest	3m 45s
PHP 8.0 \| WP latest \| highest	2m 32s
PHP 8.0 \| WP latest \| lowest	2m 54s
PHP 8.0 \| WP latest (MS) \| highest	3m 7s
PHP 8.0 \| WP latest (MS) \| lowest	3m 25s
PHP 8.1 \| WP latest \| highest	2m 24s
PHP 8.1 \| WP latest \| lowest	2m 31s
PHP 8.1 \| WP latest (MS) \| highest	3m 19s
PHP 8.1 \| WP latest (MS) \| lowest	2m 59s
PHP 7.4 \| WP trunk \| highest	3m 5s
PHP 8.0 \| WP latest \| prefer-stable	2m 24s
PHP 8.0 \| WP latest \| prefer-lowest	3m 1s
PHP 8.1 \| WP latest \| prefer-stable	2m 22s
PHP 8.1 \| WP latest \| prefer-lowest	2m 21s
PHP 8.1 \| WP trunk \| highest	3m 30s
PHP 8.2 \| WP trunk \| highest	3m 20s
PHP 7.4 (Imagick) \| WP latest \| highest	2m 27s
PHP 7.4 (with coverage) \| WP latest \| highest	5m 2s
	1h 14m 7s

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