chore: Remove unused pin_alt.svg icon (#17450)

Follow-up to https://github.com/zed-industries/zed/pull/17445

Release Notes:

- N/A

assets/icons/pin_alt.svg

@@ -1,4 +0,0 @@
-<svg width="16" height="16" viewBox="0 0 16 16" fill="none" xmlns="http://www.w3.org/2000/svg">
-<path d="M8 10V13" stroke="black" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round"/>
-<path d="M6.71429 7.088C6.7142 7.26164 6.66963 7.43181 6.58559 7.57938C6.50156 7.72695 6.38138 7.84606 6.23857 7.92333L5.47571 8.34333C5.33291 8.4206 5.21273 8.53972 5.12869 8.68729C5.04465 8.83486 5.00008 9.00503 5 9.17867V9.53333C5 9.6571 5.04515 9.7758 5.12553 9.86332C5.2059 9.95083 5.31491 10 5.42857 10H10.5714C10.6851 10 10.7941 9.95083 10.8745 9.86332C10.9548 9.7758 11 9.6571 11 9.53333V9.17867C10.9999 9.00503 10.9553 8.83486 10.8713 8.68729C10.7873 8.53972 10.6671 8.4206 10.5243 8.34333L9.76143 7.92333C9.61862 7.84606 9.49844 7.72695 9.41441 7.57938C9.33037 7.43181 9.2858 7.26164 9.28571 7.088V5.33333C9.28571 5.20957 9.33087 5.09087 9.41124 5.00335C9.49161 4.91583 9.60062 4.86667 9.71429 4.86667C9.94161 4.86667 10.1596 4.76833 10.3204 4.5933C10.4811 4.41827 10.5714 4.18087 10.5714 3.93333C10.5714 3.6858 10.4811 3.4484 10.3204 3.27337C10.1596 3.09833 9.94161 3 9.71429 3H6.28571C6.05839 3 5.84037 3.09833 5.67962 3.27337C5.51888 3.4484 5.42857 3.6858 5.42857 3.93333C5.42857 4.18087 5.51888 4.41827 5.67962 4.5933C5.84037 4.76833 6.05839 4.86667 6.28571 4.86667C6.39938 4.86667 6.50839 4.91583 6.58876 5.00335C6.66913 5.09087 6.71429 5.20957 6.71429 5.33333V7.088Z" fill="black" stroke="black" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round"/>
-</svg>