Keyboard: KC60se matrix fixes (#3446)

Keyboard: KC60se matrix fixes (#3446)

* Replace KC_NO with ___ in matrices for readability

* Add K49 to LAYOUT matrix

K49 was previously was stated to be padless, but it's actually the right-hand half of a split Backspace.

* Switched positions of K3C and K3D in LAYOUT matrix

When using a split right Shift, K3D is to the left of K3C.

* Insert KC_NO (___) element into bottom row of LAYOUT_60_ansi matrix

Reported by @NimMooMoo on QMK Discord

Right-hand modifiers on bottom row were shifted one key to the right. After debugging, discovered that the "electrical matrix" (the part of the matrix macro that determines which row and column a key uses) was one element short on the last row at K49, causing the rest of the row to be offset by one column.

This commit corrects that issue.

* Added a missing comma in the LAYOUT matrix