xml: Remove duplicate EP for separate shader ext.

The glProgramUniformMatrix4fvEXT entry point was listed in a second
require block that listed the entry point as depending on GLES 3.0
or GL_NV_non_square_matrices.

Fixes #443

xml/gl.xml

diff --git a/xml/gl.xml b/xml/gl.xml
index c573573..56513b5 100644
--- a/xml/gl.xml
+++ b/xml/gl.xml
@@ -46183,7 +46183,6 @@
                 <command name="glProgramUniform2uivEXT"/>
                 <command name="glProgramUniform3uivEXT"/>
                 <command name="glProgramUniform4uivEXT"/>
-                <command name="glProgramUniformMatrix4fvEXT"/>
                 <command name="glProgramUniformMatrix2x3fvEXT"/>
                 <command name="glProgramUniformMatrix3x2fvEXT"/>
                 <command name="glProgramUniformMatrix2x4fvEXT"/>