The ornamental design for a flexiblesheet, as shown and described.
FIG. 1 is a plan view of a flexible sheet; and,
FIG. 2 is a cross-section of the detail of the flexible sheet of FIG. 1 taken along line 2-2.
The broken lines illustrate portions of the embodiments of the flexible sheet that form no part of the claimed design. The flexible sheet includes a regular repeating pattern in length and width directions.