Revert "Bind non-keypad +/-/* to font adjustments: Bug #731244"

This reverts commit 540c64894e2c381c39f0e5e6bd720f609eddd901 due to
introducing (aggravating) bug #737236.
Revert "Compile with Vala 0.24: Bug #737227"

This reverts commit 71bd1403cce25ae68848b537f9c26b020e10f2b2 now
unnecessary due to revert in previous commit.