Embedding Projector: remove knn gpu splitting

[alicialics]

• Motivation for features / changes

Splitting an arbitrary vector into 256 parts hurts performance. This change speeds up KNN computation by 3x-5x. The splitting needs to be done before matrix multiplication step for the cosine similarity computation. Splitting at knn step is already too late. The matrix limit is 2^13 x 2^13 on firefox and 2^14 x 2^14 on chrome (gl.MAX_TEXTURE_SIZE)

• Technical description of changes Remove all code that relates to GPU splitting

• Screenshots of UI changes

• Detailed steps to verify changes work correctly (as executed by you) Ran vz_projector_test

• Alternate designs / implementations considered