Merge: Remove tex2lyx defines to allow for newer automake

Merge: Remove tex2lyx defines to allow for newer automake

Automake version 1.14 warns that subdir-objects needs to be
enabled to avoid future incompatibilities. However, this causes problems
for objects that are compiled twice (for LyX and tex2lyx) with different
defines (e.g., TEX2LYX and NO_LAYOUT_CSS). Therefore, we need to properly
fix the code without using these defines.

See also:
 - commit 16cdf70d (Jul 26, 2013),
 - commit 3698fde0 (Aug 19, 2013), and
 - http://marc.info/?l=lyx-devel&m=137673178123427&w=2.