Remove *.pot files and ignore them now.

The .pot files can be generated automatically and the files contain
timestamps in their content. They can cause huge conflicts and take huge
space even if you are not a translator.

This commit is a part of improvement discussed on
#11383 .

Signed-off-by: OGINO Masanori <masanori.ogino@gmail.com>

Author: omasanori

.gitignore

@@ -95,3 +95,4 @@ src/etc/dl
 build/
 i686-pc-mingw32/
 src/librustc/lib/llvmdeps.rs
+*.pot