Revert "Support overwriting an arbitrary number of literal bits."

This reverts commit 133c57c3,
which appears to cause test failures in
AV1/AVxEncoderThreadTest.EncoderResultTest/*

Change-Id: I200b7a135ed65dc2c3f23b23b8c3dbf0872715fa

aom_dsp/bitwriter_buffer.c

@@ -23,8 +23,12 @@ void aom_wb_write_bit(struct aom_write_bit_buffer *wb, int bit) {
   const int off = (int)wb->bit_offset;
   const int p = off / CHAR_BIT;
   const int q = CHAR_BIT - 1 - off % CHAR_BIT;
-  wb->bit_buffer[p] &= ~(1 << q);
-  wb->bit_buffer[p] |= bit << q;
+  if (q == CHAR_BIT - 1) {
+    wb->bit_buffer[p] = bit << q;
+  } else {
+    wb->bit_buffer[p] &= ~(1 << q);
+    wb->bit_buffer[p] |= bit << q;
+  }
   wb->bit_offset = off + 1;
 }